write-after-read-protocol/sql/item_func.cc at master · FlashSQL/write-after-read-protocol · GitHub

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This program is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; version 2 of the License.

This program is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */

/**

@file

@brief

This file defines all numerical functions

#include "item_func.h"

#include "my_bit.h" // my_count_bits

#include "auth_common.h" // check_password_strength

#include "binlog.h" // mysql_bin_log

#include "debug_sync.h" // DEBUG_SYNC

#include "item_cmpfunc.h" // get_datetime_value

#include "item_strfunc.h" // Item_func_geohash

#include <mysql/service_thd_wait.h>

#include "parse_tree_helpers.h" // PT_item_list

#include "rpl_mi.h" // Master_info

#include "rpl_msr.h" // channel_map

#include "rpl_rli.h" // Relay_log_info

#include "sp.h" // sp_find_routine

#include "sp_head.h" // sp_name

#include "sql_audit.h" // audit_global_variable

#include "sql_base.h" // Internal_error_handler_holder

#include "sql_class.h" // THD

#include "sql_optimizer.h" // JOIN

#include "sql_parse.h" // check_stack_overrun

#include "sql_show.h" // append_identifier

#include "sql_time.h" // TIME_from_longlong_packed

#include "strfunc.h" // find_type

#include "item_json_func.h" // Item_func_json_quote

#include <cfloat> // DBL_DIG

using std::min;

using std::max;

bool check_reserved_words(LEX_STRING *name)

{

if (!my_strcasecmp(system_charset_info, name->str, "GLOBAL") ||

!my_strcasecmp(system_charset_info, name->str, "LOCAL") ||

!my_strcasecmp(system_charset_info, name->str, "SESSION"))

return TRUE;

return FALSE;

}

/**

Evaluate a constant condition, represented by an Item tree

@param thd Thread handler

@param cond The constant condition to evaluate

@param[out] value Returned value, either true or false

@returns false if evaluation is successful, true otherwise

bool eval_const_cond(THD *thd, Item *cond, bool *value)

{

DBUG_ASSERT(cond->const_item());

*value= cond->val_int();

return thd->is_error();

}

/**

Test if the sum of arguments overflows the ulonglong range.

static inline bool test_if_sum_overflows_ull(ulonglong arg1, ulonglong arg2)

{

return ULLONG_MAX - arg1 < arg2;

}

void Item_func::set_arguments(List<Item> &list, bool context_free)

{

allowed_arg_cols= 1;

arg_count=list.elements;

args= tmp_arg; // If 2 arguments

if (arg_count <= 2 || (args=(Item**) sql_alloc(sizeof(Item*)*arg_count)))

{

List_iterator_fast<Item> li(list);

Item *item;

Item **save_args= args;

while ((item=li++))

{

*(save_args++)= item;

if (!context_free)

with_sum_func|= item->with_sum_func;

}

else

arg_count= 0; // OOM

list.empty(); // Fields are used

}

Item_func::Item_func(List<Item> &list)

:allowed_arg_cols(1)

{

set_arguments(list, false);

}

Item_func::Item_func(const POS &pos, PT_item_list *opt_list)

: super(pos), allowed_arg_cols(1)

{

if (opt_list == NULL)

{

args= tmp_arg;

arg_count= 0;

}

else

set_arguments(opt_list->value, true);

}

Item_func::Item_func(THD *thd, Item_func *item)

:Item_result_field(thd, item),

const_item_cache(0),

allowed_arg_cols(item->allowed_arg_cols),

used_tables_cache(item->used_tables_cache),

not_null_tables_cache(item->not_null_tables_cache),

arg_count(item->arg_count)

{

if (arg_count)

{

if (arg_count <=2)

args= tmp_arg;

else

{

if (!(args=(Item**) thd->alloc(sizeof(Item*)*arg_count)))

return;

}

memcpy((char*) args, (char*) item->args, sizeof(Item*)*arg_count);

}

bool Item_func::itemize(Parse_context *pc, Item **res)

{

if (skip_itemize(res))

return false;

if (super::itemize(pc, res))

return true;

with_sum_func= 0;

const bool no_named_params= !may_have_named_parameters();

for (size_t i= 0; i < arg_count; i++)

{

with_sum_func|= args[i]->with_sum_func;

if (args[i]->itemize(pc, &args[i]))

return true;

if (no_named_params && !args[i]->item_name.is_autogenerated())

{

my_error(functype() == FUNC_SP ? ER_WRONG_PARAMETERS_TO_STORED_FCT

: ER_WRONG_PARAMETERS_TO_NATIVE_FCT,

MYF(0), func_name());

return true;

}

return false;

}

Resolve references to table column for a function and its argument

SYNOPSIS:

fix_fields()

thd Thread object

ref Pointer to where this object is used. This reference

is used if we want to replace this object with another

one (for example in the summary functions).

DESCRIPTION

Call fix_fields() for all arguments to the function. The main intention

is to allow all Item_field() objects to setup pointers to the table fields.

Sets as a side effect the following class variables:

maybe_null Set if any argument may return NULL

with_sum_func Set if any of the arguments contains a sum function

used_tables_cache Set to union of the tables used by arguments

str_value.charset If this is a string function, set this to the

character set for the first argument.

If any argument is binary, this is set to binary

If for any item any of the defaults are wrong, then this can

be fixed in the fix_length_and_dec() function that is called

after this one or by writing a specialized fix_fields() for the

item.

RETURN VALUES

FALSE ok

TRUE Got error. Stored with my_error().

bool

Item_func::fix_fields(THD *thd, Item **ref)

{

DBUG_ASSERT(fixed == 0 || basic_const_item());

Item **arg,**arg_end;

uchar buff[STACK_BUFF_ALLOC]; // Max argument in function

Semi-join flattening should only be performed for top-level

predicates. Disable it for predicates that live under an

Item_func.

Disable_semijoin_flattening DSF(thd->lex->current_select(), true);

used_tables_cache= get_initial_pseudo_tables();

not_null_tables_cache= 0;

const_item_cache=1;

Use stack limit of STACK_MIN_SIZE * 2 since

on some platforms a recursive call to fix_fields

requires more than STACK_MIN_SIZE bytes (e.g. for

MIPS, it takes about 22kB to make one recursive

call to Item_func::fix_fields())

if (check_stack_overrun(thd, STACK_MIN_SIZE * 2, buff))

return TRUE; // Fatal error if flag is set!

if (arg_count)

{ // Print purify happy

for (arg=args, arg_end=args+arg_count; arg != arg_end ; arg++)

{

if (fix_func_arg(thd, arg))

return true;

}

fix_length_and_dec();

if (thd->is_error()) // An error inside fix_length_and_dec occured

return TRUE;

fixed= 1;

return FALSE;

}

bool Item_func::fix_func_arg(THD *thd, Item **arg)

{

if ((!(*arg)->fixed && (*arg)->fix_fields(thd, arg)))

return true; /* purecov: inspected */

Item *item= *arg;

if (allowed_arg_cols)

{

if (item->check_cols(allowed_arg_cols))

return true;

}

else

{

/* we have to fetch allowed_arg_cols from first argument */

DBUG_ASSERT(arg == args); // it is first argument

allowed_arg_cols= item->cols();

DBUG_ASSERT(allowed_arg_cols); // Can't be 0 any more

}

maybe_null|= item->maybe_null;

with_sum_func|= item->with_sum_func;

used_tables_cache|= item->used_tables();

not_null_tables_cache|= item->not_null_tables();

const_item_cache&= item->const_item();

with_subselect|= item->has_subquery();

with_stored_program|= item->has_stored_program();

return false;

}

void Item_func::fix_after_pullout(st_select_lex *parent_select,

st_select_lex *removed_select)

{

if (const_item())

{

Pulling out a const item changes nothing to it. Moreover, some items may

have decided that they're const by some other logic than the generic

one below, and we must preserve that decision.

return;

}

Item **arg,**arg_end;

used_tables_cache= get_initial_pseudo_tables();

not_null_tables_cache= 0;

const_item_cache=1;

if (arg_count)

{

for (arg=args, arg_end=args+arg_count; arg != arg_end ; arg++)

{

Item *const item= *arg;

item->fix_after_pullout(parent_select, removed_select);

used_tables_cache|= item->used_tables();

not_null_tables_cache|= item->not_null_tables();

const_item_cache&= item->const_item();

}

bool Item_func::walk(Item_processor processor, enum_walk walk, uchar *argument)

{

if ((walk & WALK_PREFIX) && (this->*processor)(argument))

return true;

Item **arg, **arg_end;

for (arg= args, arg_end= args+arg_count; arg != arg_end; arg++)

{

if ((*arg)->walk(processor, walk, argument))

return true;

}

return (walk & WALK_POSTFIX) && (this->*processor)(argument);

}

void Item_func::traverse_cond(Cond_traverser traverser,

void *argument, traverse_order order)

{

if (arg_count)

{

Item **arg,**arg_end;

switch (order) {

case(PREFIX):

(*traverser)(this, argument);

for (arg= args, arg_end= args+arg_count; arg != arg_end; arg++)

{

(*arg)->traverse_cond(traverser, argument, order);

}

break;

case (POSTFIX):

for (arg= args, arg_end= args+arg_count; arg != arg_end; arg++)

{

(*arg)->traverse_cond(traverser, argument, order);

}

(*traverser)(this, argument);

}

else

(*traverser)(this, argument);

}

/**

Transform an Item_func object with a transformer callback function.

The function recursively applies the transform method to each

argument of the Item_func node.

If the call of the method for an argument item returns a new item

the old item is substituted for a new one.

After this the transformer is applied to the root node

of the Item_func object.

@param transformer the transformer callback function to be applied to

the nodes of the tree of the object

@param argument parameter to be passed to the transformer

@return

Item returned as the result of transformation of the root node

Item *Item_func::transform(Item_transformer transformer, uchar *argument)

{

DBUG_ASSERT(!current_thd->stmt_arena->is_stmt_prepare());

if (arg_count)

{

Item **arg,**arg_end;

for (arg= args, arg_end= args+arg_count; arg != arg_end; arg++)

{

Item *new_item= (*arg)->transform(transformer, argument);

if (!new_item)

return 0;

THD::change_item_tree() should be called only if the tree was

really transformed, i.e. when a new item has been created.

Otherwise we'll be allocating a lot of unnecessary memory for

change records at each execution.

if (*arg != new_item)

current_thd->change_item_tree(arg, new_item);

}

return (this->*transformer)(argument);

}

/**

Compile Item_func object with a processor and a transformer

callback functions.

First the function applies the analyzer to the root node of

the Item_func object. Then if the analizer succeeeds (returns TRUE)

the function recursively applies the compile method to each argument

of the Item_func node.

If the call of the method for an argument item returns a new item

the old item is substituted for a new one.

After this the transformer is applied to the root node

of the Item_func object.

@param analyzer the analyzer callback function to be applied to the

nodes of the tree of the object

@param[in,out] arg_p parameter to be passed to the processor

@param transformer the transformer callback function to be applied to the

nodes of the tree of the object

@param arg_t parameter to be passed to the transformer

@return Item returned as result of transformation of the node,

the same item if no transformation applied, or NULL if

transformation caused an error.

Item *Item_func::compile(Item_analyzer analyzer, uchar **arg_p,

Item_transformer transformer, uchar *arg_t)

{

if (!(this->*analyzer)(arg_p))

return this;

if (arg_count)

{

Item **arg,**arg_end;

for (arg= args, arg_end= args+arg_count; arg != arg_end; arg++)

{

The same parameter value of arg_p must be passed

to analyze any argument of the condition formula.

uchar *arg_v= *arg_p;

Item *new_item= (*arg)->compile(analyzer, &arg_v, transformer, arg_t);

if (new_item == NULL)

return NULL;

if (*arg != new_item)

current_thd->change_item_tree(arg, new_item);

}

return (this->*transformer)(arg_t);

}

/**

See comments in Item_cmp_func::split_sum_func()

void Item_func::split_sum_func(THD *thd, Ref_ptr_array ref_pointer_array,

List<Item> &fields)

{

Item **arg, **arg_end;

for (arg= args, arg_end= args+arg_count; arg != arg_end ; arg++)

(*arg)->split_sum_func2(thd, ref_pointer_array, fields, arg, TRUE);

}

void Item_func::update_used_tables()

{

used_tables_cache= get_initial_pseudo_tables();

const_item_cache=1;

with_subselect= false;

with_stored_program= false;

for (uint i=0 ; i < arg_count ; i++)

{

args[i]->update_used_tables();

used_tables_cache|=args[i]->used_tables();

const_item_cache&=args[i]->const_item();

with_subselect|= args[i]->has_subquery();

with_stored_program|= args[i]->has_stored_program();

}

void Item_func_sp::fix_after_pullout(SELECT_LEX *parent_select,

SELECT_LEX *removed_select)

{

Item_func::fix_after_pullout(parent_select, removed_select);

Prevents function from being evaluated before it is locked.

@todo - make this dependent on READS SQL or MODIFIES SQL.

Due to a limitation in how functions are evaluated, we need to

ensure that we are in a prelocked mode even though the function

doesn't reference any tables.

used_tables_cache|= PARAM_TABLE_BIT;

}

table_map Item_func::used_tables() const

{

return used_tables_cache;

}

table_map Item_func::not_null_tables() const

{

return not_null_tables_cache;

}

void Item_func::print(String *str, enum_query_type query_type)

{

str->append(func_name());

str->append('(');

print_args(str, 0, query_type);

str->append(')');

}

void Item_func::print_args(String *str, uint from, enum_query_type query_type)

{

for (uint i=from ; i < arg_count ; i++)

{

if (i != from)

str->append(',');

args[i]->print(str, query_type);

}

void Item_func::print_op(String *str, enum_query_type query_type)

{

str->append('(');

for (uint i=0 ; i < arg_count-1 ; i++)

{

args[i]->print(str, query_type);

str->append(' ');

str->append(func_name());

str->append(' ');

}

args[arg_count-1]->print(str, query_type);

str->append(')');

}

/// @note Please keep in sync with Item_sum::eq().

bool Item_func::eq(const Item *item, bool binary_cmp) const

{

/* Assume we don't have rtti */

if (this == item)

return 1;

if (item->type() != FUNC_ITEM)

return 0;

Item_func *item_func=(Item_func*) item;

Item_func::Functype func_type;

if ((func_type= functype()) != item_func->functype() ||

arg_count != item_func->arg_count ||

(func_type != Item_func::FUNC_SP &&

func_name() != item_func->func_name()) ||

(func_type == Item_func::FUNC_SP &&

my_strcasecmp(system_charset_info, func_name(), item_func->func_name())))

return 0;

for (uint i=0; i < arg_count ; i++)

if (!args[i]->eq(item_func->args[i], binary_cmp))

return 0;

return 1;

}

Field *Item_func::tmp_table_field(TABLE *table)

{

Field *field= NULL;

switch (result_type()) {

case INT_RESULT:

if (max_char_length() > MY_INT32_NUM_DECIMAL_DIGITS)

field= new Field_longlong(max_char_length(), maybe_null, item_name.ptr(),

unsigned_flag);

else

field= new Field_long(max_char_length(), maybe_null, item_name.ptr(),

unsigned_flag);

break;

case REAL_RESULT:

field= new Field_double(max_char_length(), maybe_null, item_name.ptr(), decimals);

break;

case STRING_RESULT:

return make_string_field(table);

break;

case DECIMAL_RESULT:

field= Field_new_decimal::create_from_item(this);

break;

case ROW_RESULT:

default:

// This case should never be chosen

DBUG_ASSERT(0);

field= 0;

break;

}

if (field)

field->init(table);

return field;

}

my_decimal *Item_func::val_decimal(my_decimal *decimal_value)

{

DBUG_ASSERT(fixed);

longlong nr= val_int();

if (null_value)

return 0; /* purecov: inspected */

int2my_decimal(E_DEC_FATAL_ERROR, nr, unsigned_flag, decimal_value);

return decimal_value;

}

type_conversion_status Item_func::save_possibly_as_json(Field *field,

bool no_conversions)

{

if (field->type() == MYSQL_TYPE_JSON)

{

// Store the value in the JSON binary format.

Field_json *f= down_cast<Field_json *>(field);

Json_wrapper wr;

val_json(&wr);

if (null_value)

return set_field_to_null(field);

field->set_notnull();

return f->store_json(&wr);

}

else

{

// TODO Convert the JSON value to text.

return Item_func::save_in_field_inner(field, no_conversions);

}

String *Item_real_func::val_str(String *str)

{

DBUG_ASSERT(fixed == 1);

double nr= val_real();

if (null_value)

return 0; /* purecov: inspected */

str->set_real(nr, decimals, collation.collation);

return str;

}

my_decimal *Item_real_func::val_decimal(my_decimal *decimal_value)

{

DBUG_ASSERT(fixed);

double nr= val_real();

if (null_value)

return 0; /* purecov: inspected */

double2my_decimal(E_DEC_FATAL_ERROR, nr, decimal_value);

return decimal_value;

}

void Item_func::fix_num_length_and_dec()

{

uint fl_length= 0;

decimals=0;

for (uint i=0 ; i < arg_count ; i++)

{

set_if_bigger(decimals,args[i]->decimals);

set_if_bigger(fl_length, args[i]->max_length);

}

max_length=float_length(decimals);

if (fl_length > max_length)

{

decimals= NOT_FIXED_DEC;

max_length= float_length(NOT_FIXED_DEC);

}

void Item_func_numhybrid::fix_num_length_and_dec()

{}

/**

Count max_length and decimals for temporal functions.

@param item Argument array

@param nitems Number of arguments in the array.

@retval False on success, true on error.

void Item_func::count_datetime_length(Item **item, uint nitems)

{

unsigned_flag= 0;

decimals= 0;

if (field_type() != MYSQL_TYPE_DATE)

{

for (uint i= 0; i < nitems; i++)

set_if_bigger(decimals,

field_type() == MYSQL_TYPE_TIME ?

item[i]->time_precision() : item[i]->datetime_precision());

}

set_if_smaller(decimals, DATETIME_MAX_DECIMALS);

uint len= decimals ? (decimals + 1) : 0;

switch (field_type())

{

case MYSQL_TYPE_DATETIME:

case MYSQL_TYPE_TIMESTAMP:

len+= MAX_DATETIME_WIDTH;

break;

case MYSQL_TYPE_DATE:

case MYSQL_TYPE_NEWDATE:

len+= MAX_DATE_WIDTH;

break;

case MYSQL_TYPE_TIME:

len+= MAX_TIME_WIDTH;

break;

default:

DBUG_ASSERT(0);

}

fix_char_length(len);

}

/**

Set max_length/decimals of function if function is fixed point and

result length/precision depends on argument ones.

@param item Argument array.

@param nitems Number of arguments in the array.

This function doesn't set unsigned_flag. Call agg_result_type()

first to do that.

void Item_func::count_decimal_length(Item **item, uint nitems)

{

int max_int_part= 0;

decimals= 0;

for (uint i=0 ; i < nitems ; i++)

{

set_if_bigger(decimals, item[i]->decimals);

set_if_bigger(max_int_part, item[i]->decimal_int_part());

}

int precision= min(max_int_part + decimals, DECIMAL_MAX_PRECISION);

fix_char_length(my_decimal_precision_to_length_no_truncation(precision,

decimals,

unsigned_flag));

}

/**

Set char_length to the maximum number of characters required by any

of this function's arguments.

This function doesn't set unsigned_flag. Call agg_result_type()

first to do that.

void Item_func::count_only_length(Item **item, uint nitems)

{

uint32 char_length= 0;

for (uint i= 0; i < nitems; i++)

set_if_bigger(char_length, item[i]->max_char_length());

fix_char_length(char_length);

}

/**

Set max_length/decimals of function if function is floating point and

result length/precision depends on argument ones.

@param item Argument array.

@param nitems Number of arguments in the array.

void Item_func::count_real_length(Item **item, uint nitems)

{

uint32 length= 0;

decimals= 0;

max_length= 0;

for (uint i=0 ; i < nitems; i++)

{

if (decimals != NOT_FIXED_DEC)

{

set_if_bigger(decimals, item[i]->decimals);

set_if_bigger(length, (item[i]->max_length - item[i]->decimals));

}

set_if_bigger(max_length, item[i]->max_length);

}

if (decimals != NOT_FIXED_DEC)

{

max_length= length;

length+= decimals;

if (length < max_length) // If previous operation gave overflow

max_length= UINT_MAX32;

else

max_length= length;

}

/**

Calculate max_length and decimals for STRING_RESULT functions.

@param field_type Field type.

@param items Argument array.

@param nitems Number of arguments.

@retval False on success, true on error.

bool Item_func::count_string_result_length(enum_field_types field_type,

Item **items, uint nitems)

{

if (agg_arg_charsets_for_string_result(collation, items, nitems))

return true;

if (is_temporal_type(field_type))

count_datetime_length(items, nitems);

else

{

decimals= NOT_FIXED_DEC;

count_only_length(items, nitems);

}

return false;

}

void Item_func::signal_divide_by_null()

{

THD *thd= current_thd;

if (thd->variables.sql_mode & MODE_ERROR_FOR_DIVISION_BY_ZERO)

push_warning(thd, Sql_condition::SL_WARNING, ER_DIVISION_BY_ZERO,

ER(ER_DIVISION_BY_ZERO));

null_value= 1;

}

void Item_func::signal_invalid_argument_for_log()

{

THD *thd= current_thd;

push_warning(thd, Sql_condition::SL_WARNING,

ER_INVALID_ARGUMENT_FOR_LOGARITHM,

ER(ER_INVALID_ARGUMENT_FOR_LOGARITHM));

null_value= TRUE;

}

Item *Item_func::get_tmp_table_item(THD *thd)

{

if (!with_sum_func && !const_item())

return new Item_field(result_field);

return copy_or_same(thd);

}

const Item_field*

Item_func::contributes_to_filter(table_map read_tables,

table_map filter_for_table,

const MY_BITMAP *fields_to_ignore) const

{

DBUG_ASSERT((read_tables & filter_for_table) == 0);

Multiple equality (Item_equal) should not call this function

because it would reject valid comparisons.

DBUG_ASSERT(functype() != MULT_EQUAL_FUNC);

To contribute to filering effect, the condition must refer to

exactly one unread table: the table filtering is currently

calculated for.

if ((used_tables() & ~read_tables) != filter_for_table)

return NULL;

Whether or not this Item_func has an operand that is a field in

'filter_for_table' that is not in 'fields_to_ignore'.

Item_field* usable_field= NULL;

Whether or not this Item_func has an operand that can be used as

available value. arg_count==1 for Items with implicit values like

"field IS NULL".

bool found_comparable= (arg_count == 1);

for (uint i= 0; i < arg_count; i++)

{

const Item::Type arg_type= args[i]->real_item()->type();

if (arg_type == Item::SUBSELECT_ITEM)

{

if (args[i]->const_item())

{

// Constant subquery, i.e., not a dependent subquery.

found_comparable= true;

continue;

}

This is either "fld OP <dependent_subquery>" or "fld BETWEEN X

and Y" where either X or Y is a dependent subquery. Filtering

effect should not be calculated for this item because the cost

of evaluating the dependent subquery is currently not

calculated and its accompanying filtering effect is too

uncertain. See WL#7384.

return NULL;

} // ... if subquery.

const table_map used_tabs= args[i]->used_tables();

if (arg_type == Item::FIELD_ITEM && (used_tabs == filter_for_table))

{

The qualifying table of args[i] is filter_for_table. args[i]

may be a field or a reference to a field, e.g. through a

view.

Item_field *fld= static_cast<Item_field*>(args[i]->real_item());

Use args[i] as value if

1) this field shall be ignored, or

2) a usable field has already been found (meaning that

this is "filter_for_table.colX OP filter_for_table.colY").

if (bitmap_is_set(fields_to_ignore, fld->field->field_index) || // 1)

usable_field) // 2)

{

found_comparable= true;

continue;

}

This field shall contribute to filtering effect if a

value is found for it

usable_field= fld;

} // if field.

else

{

It's not a subquery. May be a function, a constant, an outer

reference, a field of another table...

Already checked that this predicate does not refer to tables

later in the join sequence. Verify it:

DBUG_ASSERT(!(used_tabs & (~read_tables & ~filter_for_table)));

found_comparable= true;

}

return (found_comparable ? usable_field : NULL);

}

/**

Return new Item_field if given expression matches GC

@see substitute_gc()

@param func Expression to be replaced

@param fld GCs field

@param type Result type to match with Field

@returns

item new Item_field for matched GC

NULL otherwise

Item_field *get_gc_for_expr(Item_func **func, Field *fld, Item_result type)

{

Item_func *expr= down_cast<Item_func*>(fld->gcol_info->expr_item);

In the case where the generated column expression returns JSON and

the predicate compares the values as strings, it is not safe to

replace the expression with the generated column, since the

indexed string values will be double-quoted. The generated column

expression should use the JSON_UNQUOTE function to strip off the

double-quotes in order to get a usable index for looking up

strings. See also the comment below.

if (type == STRING_RESULT && expr->field_type() == MYSQL_TYPE_JSON)

return NULL;

Skip unquoting function. This is needed to address JSON string

comparison issue. All JSON_* functions return quoted strings. In

order to create usable index, GC column expression has to include

JSON_UNQUOTE function, e.g JSON_UNQUOTE(JSON_EXTRACT(..)).

Hence, the unquoting function in column expression have to be

skipped in order to correctly match GC expr to expr in

WHERE condition. The exception is if user has explicitly used

JSON_UNQUOTE in WHERE condition.

if (!strcmp(expr->func_name(),"json_unquote") &&

strcmp((*func)->func_name(),"json_unquote"))

{

if (!expr->arguments()[0]->can_be_substituted_for_gc())

return NULL;

expr= down_cast<Item_func*>(expr->arguments()[0]);

}

DBUG_ASSERT(expr->can_be_substituted_for_gc());

View remainder of file in raw view

write-after-read-protocol/sql/item_func.cc at master · FlashSQL/write-after-read-protocol · GitHub

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