schema-object-names.md

title	summary	aliases
Schema Object Names	Learn about schema object names in TiDB SQL statements.	/docs/dev/schema-object-names/ /docs/dev/reference/sql/language-structure/schema-object-names/

Schema Object Names

This document introduces schema object names in TiDB SQL statements.

Schema object names are used to name all schema objects in TiDB, including database, table, index, column, and alias. You can quote these objects using identifiers in SQL statements.

You can use backticks to enclose the identifier. For example, SELECT * FROM t can also be written as SELECT * FROM `t`. But if the identifier includes one or more special characters or is a reserved keyword, it must be enclosed in backticks to quote the schema object it represents.

{{< copyable "sql" >}}

SELECT * FROM `table` WHERE `table`.id = 20;

If you set ANSI_QUOTES in SQL MODE, TiDB will recognize the string enclosed in double quotation marks " as an identifier.

{{< copyable "sql" >}}

CREATE TABLE "test" (a varchar(10));

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your TiDB version for the right syntax to use line 1 column 19 near ""test" (a varchar(10))" 

{{< copyable "sql" >}}

SET SESSION sql_mode='ANSI_QUOTES';

Query OK, 0 rows affected (0.000 sec)

{{< copyable "sql" >}}

CREATE TABLE "test" (a varchar(10));

Query OK, 0 rows affected (0.012 sec)

If you want to use the backtick character in the quoted identifier, repeat the backtick twice. For example, to create a table a`b:

{{< copyable "sql" >}}

CREATE TABLE `a``b` (a int);

In a SELECT statement, you can use an identifier or a string to specify an alias:

{{< copyable "sql" >}}

SELECT 1 AS `identifier`, 2 AS 'string';

+------------+--------+
| identifier | string |
+------------+--------+
|          1 |      2 |
+------------+--------+
1 row in set (0.00 sec)

For more information, see MySQL Schema Object Names.

Identifier qualifiers

Object names can be unqualified or qualified. For example, the following statement creates a table without a qualified name:

{{< copyable "sql" >}}

CREATE TABLE t (i int);

If you have not used the USE statement or the connection parameter to configure the database, the ERROR 1046 (3D000): No database selected error is displayed. At this time, you can specify the database qualified name:

{{< copyable "sql" >}}

CREATE TABLE test.t (i int);

White spaces can exist around .. table_name.col_name and table_name . col_name are equivalent.

To quote this identifier, use:

{{< copyable "sql" >}}

`table_name`.`col_name`

Instead of:

`table_name.col_name`

For more information, see MySQL Identifier Qualifiers.