sqlancer
diff --git a/src/sqlancer/common/gen/AbstractTableGenerator.java b/src/sqlancer/common/gen/AbstractTableGenerator.java
@@ -0,0 +1,77 @@
+package sqlancer.common.gen;
+
+import java.util.List;
+
+import sqlancer.common.schema.AbstractTableColumn;
+
+public abstract class AbstractTableGenerator<C extends AbstractTableColumn<?, ?>> extends AbstractGenerator {
+
+    /**
+     * Appends {@code CREATE TABLE <name>}.
+     *
+     * @param tableName
+     *            the name of the table to create.
+     */
+    protected void appendCreateTable(String tableName) {
+        appendCreateTable(tableName, false);
+    }
+
+    /**
+     * Appends {@code CREATE TABLE [IF NOT EXISTS ]<name>}.
+     *
+     * @param tableName
+     *            the name of the table to create.
+     * @param ifNotExists
+     *            whether to emit the {@code IF NOT EXISTS} clause.
+     */
+    protected void appendCreateTable(String tableName, boolean ifNotExists) {
+        sb.append("CREATE TABLE ");
+        if (ifNotExists) {
+            sb.append("IF NOT EXISTS ");
+        }
+        sb.append(tableName);
+    }
+
+    /**
+     * Appends a parenthesized, comma-separated column definition list, e.g. {@code (c0 INT, c1 TEXT)}. Delegates each
+     * column's rendering to {@link #appendColumnDefinition(AbstractTableColumn)}.
+     *
+     * @param columns
+     *            the columns to render.
+     */
+    protected void appendColumnDefinitions(List<C> columns) {
+        sb.append("(");
+        appendColumnDefinitionList(columns);
+        sb.append(")");
+    }
+
+    /**
+     * Appends a comma-separated column definition list without enclosing parentheses, e.g. {@code c0 INT, c1 TEXT}.
+     * Useful when subclasses also emit table-level constraints (e.g. {@code PRIMARY KEY (...)}) inside the same parens.
+     *
+     * @param columns
+     *            the columns to render.
+     */
+    protected void appendColumnDefinitionList(List<C> columns) {
+        for (int i = 0; i < columns.size(); i++) {
+            if (i != 0) {
+                sb.append(", ");
+            }
+            appendColumnDefinition(columns.get(i));
+        }
+    }
+
+    /**
+     * Appends a single column's definition. Default output is {@code <name> <type>}, e.g. {@code c0 INT}. Override to
+     * add constraints such as {@code NOT NULL}, {@code DEFAULT ...}, or {@code CHECK (...)}.
+     *
+     * @param column
+     *            the column whose definition to render.
+     */
+    protected void appendColumnDefinition(C column) {
+        sb.append(column.getName());
+        sb.append(" ");
+        sb.append(column.getType());
+    }
+
+}
diff --git a/src/sqlancer/databend/gen/DatabendTableGenerator.java b/src/sqlancer/databend/gen/DatabendTableGenerator.java
@@ -4,8 +4,8 @@
 import java.util.List;
 
 import sqlancer.Randomly;
+import sqlancer.common.gen.AbstractTableGenerator;
 import sqlancer.common.gen.TypedExpressionGenerator;
-import sqlancer.common.query.ExpectedErrors;
 import sqlancer.common.query.SQLQueryAdapter;
 import sqlancer.databend.DatabendErrors;
 import sqlancer.databend.DatabendProvider.DatabendGlobalState;
@@ -15,44 +15,49 @@
 import sqlancer.databend.DatabendToStringVisitor;
 import sqlancer.databend.ast.DatabendExpression;
 
-public class DatabendTableGenerator {
+public class DatabendTableGenerator extends AbstractTableGenerator<DatabendColumn> {
+
+    private DatabendGlobalState globalState;
+    private TypedExpressionGenerator<DatabendExpression, DatabendColumn, DatabendDataType> gen;
+
+    public DatabendTableGenerator() {
+        this.canAffectSchema = true;
+    }
 
     public SQLQueryAdapter getQuery(DatabendGlobalState globalState) {
-        ExpectedErrors errors = new ExpectedErrors();
+        this.globalState = globalState;
+        return getStatement();
+    }
+
+    @Override
+    public void buildStatement() {
         DatabendErrors.addExpressionErrors(errors);
-        StringBuilder sb = new StringBuilder();
         String tableName = globalState.getSchema().getFreeTableName();
-        sb.append("CREATE TABLE ");
-        sb.append(tableName);
-        sb.append("(");
+        appendCreateTable(tableName);
         List<DatabendColumn> columns = getNewColumns();
-        TypedExpressionGenerator<DatabendExpression, DatabendColumn, DatabendDataType> gen = new DatabendNewExpressionGenerator(
-                globalState).setColumns(columns);
-        for (int i = 0; i < columns.size(); i++) {
-            if (i != 0) {
-                sb.append(", ");
-            }
-            sb.append(columns.get(i).getName());
-            sb.append(" ");
-            sb.append(columns.get(i).getType());
+        gen = new DatabendNewExpressionGenerator(globalState).setColumns(columns);
+        appendColumnDefinitions(columns);
+    }
 
-            if (globalState.getDbmsSpecificOptions().testNotNullConstraints
-                    && Randomly.getBooleanWithRatherLowProbability()) {
-                sb.append(" NOT NULL");
-            } else {
-                sb.append(" NULL"); // Databend 默认字段为非空，这个将它默认设置为允许空
-            }
+    @Override
+    protected void appendColumnDefinition(DatabendColumn column) {
+        sb.append(column.getName());
+        sb.append(" ");
+        sb.append(column.getType());
 
-            if (Randomly.getBoolean() && globalState.getDbmsSpecificOptions().testDefaultValues) {
-                sb.append(" DEFAULT(");
-                sb.append(DatabendToStringVisitor.asString(// 常量类型于字段类型等同
-                        gen.generateConstant(columns.get(i).getType().getPrimitiveDataType())));
-                sb.append(")");
-            }
+        if (globalState.getDbmsSpecificOptions().testNotNullConstraints
+                && Randomly.getBooleanWithRatherLowProbability()) {
+            sb.append(" NOT NULL");
+        } else {
+            sb.append(" NULL"); // Databend 默认字段为非空，这个将它默认设置为允许空
         }
 
-        sb.append(")");
-        return new SQLQueryAdapter(sb.toString(), errors, true);
+        if (Randomly.getBoolean() && globalState.getDbmsSpecificOptions().testDefaultValues) {
+            sb.append(" DEFAULT(");
+            sb.append(DatabendToStringVisitor.asString(// 常量类型于字段类型等同
+                    gen.generateConstant(column.getType().getPrimitiveDataType())));
+            sb.append(")");
+        }
     }
 
     private static List<DatabendColumn> getNewColumns() {

diff --git a/src/sqlancer/duckdb/gen/DuckDBTableGenerator.java b/src/sqlancer/duckdb/gen/DuckDBTableGenerator.java
@@ -5,8 +5,8 @@
 import java.util.stream.Collectors;
 
 import sqlancer.Randomly;
+import sqlancer.common.gen.AbstractTableGenerator;
 import sqlancer.common.gen.UntypedExpressionGenerator;
-import sqlancer.common.query.ExpectedErrors;
 import sqlancer.common.query.SQLQueryAdapter;
 import sqlancer.duckdb.DuckDBErrors;
 import sqlancer.duckdb.DuckDBProvider.DuckDBGlobalState;
@@ -16,50 +16,28 @@
 import sqlancer.duckdb.DuckDBToStringVisitor;
 import sqlancer.duckdb.ast.DuckDBExpression;
 
-public class DuckDBTableGenerator {
+public class DuckDBTableGenerator extends AbstractTableGenerator<DuckDBColumn> {
+
+    private DuckDBGlobalState globalState;
+    private UntypedExpressionGenerator<DuckDBExpression, DuckDBColumn> gen;
+
+    public DuckDBTableGenerator() {
+        this.canAffectSchema = true;
+    }
 
     public SQLQueryAdapter getQuery(DuckDBGlobalState globalState) {
-        ExpectedErrors errors = new ExpectedErrors();
-        StringBuilder sb = new StringBuilder();
+        this.globalState = globalState;
+        return getStatement();
+    }
+
+    @Override
+    public void buildStatement() {
         String tableName = globalState.getSchema().getFreeTableName();
-        sb.append("CREATE TABLE ");
-        sb.append(tableName);
-        sb.append("(");
+        appendCreateTable(tableName);
         List<DuckDBColumn> columns = getNewColumns();
-        UntypedExpressionGenerator<DuckDBExpression, DuckDBColumn> gen = new DuckDBExpressionGenerator(globalState)
-                .setColumns(columns);
-        for (int i = 0; i < columns.size(); i++) {
-            if (i != 0) {
-                sb.append(", ");
-            }
-            sb.append(columns.get(i).getName());
-            sb.append(" ");
-            sb.append(columns.get(i).getType());
-            if (globalState.getDbmsSpecificOptions().testCollate && Randomly.getBooleanWithRatherLowProbability()
-                    && columns.get(i).getType().getPrimitiveDataType() == DuckDBDataType.VARCHAR) {
-                sb.append(" COLLATE ");
-                sb.append(getRandomCollate());
-            }
-            if (globalState.getDbmsSpecificOptions().testIndexes && Randomly.getBooleanWithRatherLowProbability()) {
-                sb.append(" UNIQUE");
-            }
-            if (globalState.getDbmsSpecificOptions().testNotNullConstraints
-                    && Randomly.getBooleanWithRatherLowProbability()) {
-                sb.append(" NOT NULL");
-            }
-            if (globalState.getDbmsSpecificOptions().testCheckConstraints
-                    && Randomly.getBooleanWithRatherLowProbability()) {
-                sb.append(" CHECK(");
-                sb.append(DuckDBToStringVisitor.asString(gen.generateExpression()));
-                DuckDBErrors.addExpressionErrors(errors);
-                sb.append(")");
-            }
-            if (Randomly.getBoolean() && globalState.getDbmsSpecificOptions().testDefaultValues) {
-                sb.append(" DEFAULT(");
-                sb.append(DuckDBToStringVisitor.asString(gen.generateConstant()));
-                sb.append(")");
-            }
-        }
+        gen = new DuckDBExpressionGenerator(globalState).setColumns(columns);
+        sb.append("(");
+        appendColumnDefinitionList(columns);
         if (globalState.getDbmsSpecificOptions().testIndexes && Randomly.getBoolean()) {
             errors.add("Invalid type for index");
             List<DuckDBColumn> primaryKeyColumns = Randomly.nonEmptySubset(columns);
@@ -68,7 +46,37 @@ public SQLQueryAdapter getQuery(DuckDBGlobalState globalState) {
             sb.append(")");
         }
         sb.append(")");
-        return new SQLQueryAdapter(sb.toString(), errors, true);
+    }
+
+    @Override
+    protected void appendColumnDefinition(DuckDBColumn column) {
+        sb.append(column.getName());
+        sb.append(" ");
+        sb.append(column.getType());
+        if (globalState.getDbmsSpecificOptions().testCollate && Randomly.getBooleanWithRatherLowProbability()
+                && column.getType().getPrimitiveDataType() == DuckDBDataType.VARCHAR) {
+            sb.append(" COLLATE ");
+            sb.append(getRandomCollate());
+        }
+        if (globalState.getDbmsSpecificOptions().testIndexes && Randomly.getBooleanWithRatherLowProbability()) {
+            sb.append(" UNIQUE");
+        }
+        if (globalState.getDbmsSpecificOptions().testNotNullConstraints
+                && Randomly.getBooleanWithRatherLowProbability()) {
+            sb.append(" NOT NULL");
+        }
+        if (globalState.getDbmsSpecificOptions().testCheckConstraints
+                && Randomly.getBooleanWithRatherLowProbability()) {
+            sb.append(" CHECK(");
+            sb.append(DuckDBToStringVisitor.asString(gen.generateExpression()));
+            DuckDBErrors.addExpressionErrors(errors);
+            sb.append(")");
+        }
+        if (Randomly.getBoolean() && globalState.getDbmsSpecificOptions().testDefaultValues) {
+            sb.append(" DEFAULT(");
+            sb.append(DuckDBToStringVisitor.asString(gen.generateConstant()));
+            sb.append(")");
+        }
     }
 
     public static String getRandomCollate() {

diff --git a/src/sqlancer/hsqldb/gen/HSQLDBTableGenerator.java b/src/sqlancer/hsqldb/gen/HSQLDBTableGenerator.java
@@ -5,44 +5,48 @@
 import javax.annotation.Nullable;
 
 import sqlancer.Randomly;
-import sqlancer.common.query.ExpectedErrors;
+import sqlancer.common.gen.AbstractTableGenerator;
 import sqlancer.common.query.SQLQueryAdapter;
 import sqlancer.hsqldb.HSQLDBProvider;
 import sqlancer.hsqldb.HSQLDBSchema;
 
-public class HSQLDBTableGenerator {
+public class HSQLDBTableGenerator extends AbstractTableGenerator<HSQLDBSchema.HSQLDBColumn> {
+
+    private HSQLDBProvider.HSQLDBGlobalState globalState;
+    private String tableName;
+
+    public HSQLDBTableGenerator() {
+        this.canAffectSchema = true;
+    }
 
     public SQLQueryAdapter getQuery(HSQLDBProvider.HSQLDBGlobalState globalState, @Nullable String tableName) {
-        ExpectedErrors errors = new ExpectedErrors();
-        StringBuilder sb = new StringBuilder();
+        this.globalState = globalState;
+        this.tableName = tableName;
+        return getStatement();
+    }
+
+    @Override
+    public void buildStatement() {
         String name = tableName;
-        if (tableName == null) {
+        if (name == null) {
             name = globalState.getSchema().getFreeTableName();
         }
-        sb.append("CREATE TABLE ");
-        if (Randomly.getBoolean()) {
-            sb.append("IF NOT EXISTS ");
-        }
-        sb.append(name);
-        sb.append("(");
-        List<HSQLDBSchema.HSQLDBColumn> columns = getNewColumns();
-        for (int i = 0; i < columns.size(); i++) {
-            if (i != 0) {
-                sb.append(", ");
-            }
-            sb.append(columns.get(i).getName());
-            sb.append(" ");
-            sb.append(columns.get(i).getType().getType().name());
-            if (columns.get(i).getType().getSize() > 0) {
-                // Cannot specify size for non composite data types
-                sb.append("(");
-                sb.append(columns.get(i).getType().getSize());
-                sb.append(")");
-            }
-        }
-        sb.append(")");
+        appendCreateTable(name, Randomly.getBoolean());
+        appendColumnDefinitions(getNewColumns());
         sb.append(";");
-        return new SQLQueryAdapter(sb.toString(), errors, true);
+    }
+
+    @Override
+    protected void appendColumnDefinition(HSQLDBSchema.HSQLDBColumn column) {
+        sb.append(column.getName());
+        sb.append(" ");
+        sb.append(column.getType().getType().name());
+        if (column.getType().getSize() > 0) {
+            // Cannot specify size for non composite data types
+            sb.append("(");
+            sb.append(column.getType().getSize());
+            sb.append(")");
+        }
     }
 
     private static List<HSQLDBSchema.HSQLDBColumn> getNewColumns() {