A Question on TiDB Syntax Compatibility

translator_bot · June 23, 2024, 6:02am

Note:
This topic has been translated from a Chinese forum by GPT and might contain errors.

Original topic: tidb 语法兼容性一问

| username: ShawnYan

To improve efficiency, please provide the following information. Clear problem descriptions can be resolved faster:

【TiDB Usage Environment】Production, Testing, Research
【TiDB Version】tidb v6.1
【Encountered Problem】tidb syntax not supported
【Reproduction Path】What operations were performed that caused the problem

(root@127.1) [test] 11:49:56> CREATE TABLE word
    -> (
    ->     id        INT PRIMARY KEY AUTO_INCREMENT,
    ->     text      VARCHAR(64),
    ->     topic_id  INT NOT NULL REFERENCES topic (id),
    ->     published DATE,
    ->     length    INT NOT NULL DEFAULT LENGTH(text),
    ->     UNIQUE KEY word_topic_text (topic_id, text),
    ->     UNIQUE KEY word_topic_published_length_uk (topic_id, published, length)
    -> ) ;
ERROR 3770 (HY000): Default value expression of column 'length' contains a disallowed function: `LENGTH`.
(root@127.1) [test] 11:50:01>

【Problem Phenomenon and Impact】

In MariaDB, the syntax DEFAULT LENGTH(text), is supported.

【Attachments】

Please provide the version information of each component, such as cdc/tikv, which can be obtained by executing cdc version/tikv-server --version.

translator_bot · June 23, 2024, 6:02am

| username: cheng | Original post link

MySQL Compatibility Reference Document Comparison with MySQL Compatibility | PingCAP Docs

translator_bot · June 23, 2024, 6:02am

| username: ShawnYan | Original post link

This situation is not documented.

translator_bot · June 23, 2024, 6:02am

| username: ShawnYan | Original post link

Compatibility issues, currently not supported.
The documentation also does not clearly specify which expressions are supported.

Currently supported expressions:

github.com

pingcap/tidb/blob/ad0f3ddcd70b10cbce1a077c6276ac5cbc8fd3a1/ddl/ddl_api.go#L1132


      
          		}
          	}
          
          	if err = processAndCheckDefaultValueAndColumn(ctx, col, outPriKeyConstraint, hasDefaultValue, setOnUpdateNow, hasNullFlag); err != nil {
          		return nil, nil, errors.Trace(err)
          	}
          	return col, constraints, nil
          }
          
          // getFuncCallDefaultValue gets the default column value of function-call expression.
          func getFuncCallDefaultValue(col *table.Column, option *ast.ColumnOption, expr *ast.FuncCallExpr) (interface{}, bool, error) {
          	switch expr.FnName.L {
          	case ast.CurrentTimestamp:
          		tp, fsp := col.FieldType.GetType(), col.FieldType.GetDecimal()
          		if tp == mysql.TypeTimestamp || tp == mysql.TypeDatetime {
          			defaultFsp := 0
          			if len(expr.Args) == 1 {
          				if val := expr.Args[0].(*driver.ValueExpr); val != nil {
          					defaultFsp = int(val.GetInt64())
          				}
          			}

getFuncCallDefaultValue

translator_bot · June 23, 2024, 6:02am

| username: system | Original post link

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