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SQL IDENTIFIERS

SQL identifiers is the name of the database objects.

Such as table, view, database these objects are examples of SQL identifiers:

Requirement​

Unquoted object identifiers:

  • Begin with a Unicode letter (A-Z, a-z) or an underscore (_). Subsequent characters can only be letters, underscores, digits (0-9), or dollar signs ($).

  • In default, Are stored and resolved as lowercase characters (e.g. ID is stored and resolved as id).

Double-quoted object Identifiers:

  • The identifier can contain and can even start with any ASCII character from the blank character (32) to the tilde (126).

  • In default, The case of the identifier is preserved when storing and resolving the identifier (e.g. "Id" is stored and resolved as Id).

Examples:

databend :) create table " with""TestQuote""" (id int);

databend :) desc ` with""TestQuote""`;
+-------+------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+------+------+---------+-------+
| id    | INT  | NO   | 0       |       |
+-------+------+------+---------+-------+

Unquoted Identifiers​

If an identifier is not enclosed in double quotes, it must begin with a letter or underscore (_) and cannot contain extended characters or blank spaces.

The following are all examples of valid identifiers; however, in default, the case of the characters in these identifiers would not be preserved:

myidentifier
MyIdentifier1
My$identifier
_my_identifier

Double-quoted Identifiers​

In default, Double-quoted identifiers are case-sensitive and can start with and contain any valid characters, including:

  • Numbers

  • Special characters (., ', !, @, #, $, %, ^, &, *, etc.)

  • Extended ASCII and non-ASCII characters

  • Blank spaces

"MyIdentifier"
"my.identifier"
"my identifier"
"My 'Identifier'"
"3rd_identifier"
"$Identifier"
"идентификатор"

Resolution​

By default, Databend applies the following rules for storing identifiers (at creation/definition time) and resolving them (in queries and other SQL statements):

  • When an identifier is unquoted, it is stored and resolved in lowercase.

  • When an identifier is double-quoted, it is stored and resolved exactly as entered, including case.

If want to preserve the case of characters when use unquoted identifier, need set unquoted_ident_case_sensitive = 1.

Examples:

databend :) set unquoted_ident_case_sensitive=1;

databend :) create table Tt(id int);

databend :) desc Tt;
+-------+------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+------+------+---------+-------+
| id    | INT  | NO   | 0       |       |
+-------+------+------+---------+-------+

databend :) create table tt(id1 int);
Query OK, 0 rows affected (0.08 sec)

databend :) desc tt;
+-------+------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+------+------+---------+-------+
| id1   | INT  | NO   | 0       |       |
+-------+------+------+---------+-------+

If do not want to preserve the case of characters when use double identifier, need set quoted_ident_case_sensitive = 0.

Examples:

databend :) set quoted_ident_case_sensitive=0;
Query OK, 0 rows affected (0.03 sec)

databend :) create table "Test"(id int);
Query OK, 0 rows affected (0.06 sec)

databend :) desc Test;
+-------+------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+------+------+---------+-------+
| id    | INT  | NO   | 0       |       |
+-------+------+------+---------+-------+

databend :) desc test;
+-------+------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+------+------+---------+-------+
| id    | INT  | NO   | 0       |       |
+-------+------+------+---------+-------+