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    PolarDB:SQL limits

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    PolarDB:SQL limits

    Last Updated:Nov 20, 2025

    PolarDB-X 1.0 is highly compatible with the MySQL protocol and the Structured Query Language (SQL) syntax of MySQL. However, some limits are imposed on the SQL statements for PolarDB-X 1.0. This is because the architecture of distributed databases differs from that of single-instance databases. This topic describes the limits of SQL statements in PolarDB-X 1.0.

    General limits on the SQL statements

    • PolarDB-X 1.0 does not support custom data types or custom functions.

    • PolarDB-X 1.0 does not support stored procedures, triggers, or cursors.

    • PolarDB-X 1.0 does not support temporary tables.

    • PolarDB-X 1.0 does not support compound statements, such as BEGIN...END, LOOP...END LOOP, REPEAT...UNTIL...END REPEAT, and WHILE...DO...END WHILE.

    • PolarDB-X 1.0 does not support flow control statements, such as IF and WHILE statements.

    • PolarDB-X 1.0 does not support foreign key.

    Limits on the SQL syntax

    • DDL

      • You cannot execute the CREATE TABLE tbl_name LIKE old_tbl_name statement for table sharding.

      • You cannot execute the CREATE TABLE tbl_name SELECT statements for table sharding.

      • You cannot execute the RENAME statement to rename multiple tables at a time.

      • You cannot execute the ALTER TABLE statement to change shard key fields.

      • PolarDB-X 1.0 does not support data definition language (DDL) operations across schemas, such as CREATE TABLE db_name.tbl_name (...).

      For more information about DDL statements, see DDL.

    • DML

      • PolarDB-X 1.0 does not support the following statements: SELECT INTO OUTFILE, INTO DUMPFILE, and INTO var_name.

      • PolarDB-X 1.0 does not support STRAIGHT_JOIN or NATURAL JOIN operations.

      • PolarDB-X 1.0 does not support subqueries in UPDATE SET clauses.

      • PolarDB-X 1.0 does not support INSERT DELAYED statements.

      • PolarDB-X 1.0 does not support variable references and operations in SQL statements. For example, you cannot execute the following statement: SET @c=1, @d=@c+1; SELECT @c, @d.

      • You cannot perform the INSERT, REPLACE, UPDATE, or DELETE operations on broadcast tables in flexible transactions.

      For more information about data manipulation language (DML) statements, see DML.

    • Subqueries

      • PolarDB-X 1.0 does not support subqueries in HAVING or JOIN ON clauses.

      • PolarDB-X 1.0 does not support the ROW functions in the scalar subqueries that use equal signs (=) as operators.

      For more information about subqueries, see Subqueries.

    • Database management

      • PolarDB-X 1.0 does not support the combination of LIMIT and COUNT in SHOW WARNINGS statements.

      • PolarDB-X 1.0 does not support the combination of LIMIT and COUNT in SHOW ERRORS statements.

    • Operators that are not supported by PolarDB-X 1.0

      PolarDB-X 1.0 does not support the assignment operators ':='

      For more information about operators, see Operators.

    • Functions that are not supported by PolarDB-X 1.0

      For more information about functions, see Functions.

    • Keywords that are not supported by PolarDB-X 1.0

      • MILLISECOND

      • MICROSECOND