Lexical structure

An SQL input consists of a sequence of commands each of which is a sequence of tokens, terminated by a semicolon (;).

The syntax of a command defines its set of valid tokens. A token can be a key word, an identifier, a quoted identifier, a literal (or constant), or a special character symbol.

Table of contents

• String literal

  • Escape strings

  • String literals with C-Style escapes

• Key words and identifiers

• Special characters

• Comments

String literal

String literals are defined as an arbitrary sequence of characters that are delimited with single quotes ' as defined in ANSI SQL, for example 'This is a string'.

Escape strings

The escape character in CrateDB is the single-quote '. A character gets escaped when adding a single-quote before it. For example a single quote character within a string literal can be included by writing two adjacent single quotes, e.g., 'Jack''s car'.

Note

Two adjacent single quotes are not equivalent to the double-quote character ".

String literals with C-Style escapes

In addition to the escaped character ', CrateDB supports C-Style escaped string sequences. Such a sequence is constructed by prefixing the string literal with the letter E or e, for example, e'hello\nWorld'. The following escaped sequences are supported:

For instance, the escape string literal e'\u0061\x61\141' is equivalent to the 'aaa' string literal.

cr> select e'\u0061\x61\141' as col1;
+------+
| col1 |
+------+
| aaa  |
+------+
SELECT 1 row in set (... sec)

Any other character following a backslash is taken literally. Thus, to include a backslash character \, two adjacent backslashes need to be used (i.e. \\).

cr> select e'aa\\nbb' as col1;
+--------+
| col1   |
+--------+
| aa\nbb |
+--------+
SELECT 1 row in set (... sec)

Finally, a single quote can be included in an escape string literal by also using the escape backslash character: \', in addition to the single-quote described in the string literals section.

cr> select e'aa\'bb' as col1;
+-------+
| col1  |
+-------+
| aa'bb |
+-------+
SELECT 1 row in set (... sec)

Key words and identifiers

The table below lists all reserved key words in CrateDB. These need to be quoted if used as identifiers:

cr> SELECT word FROM pg_catalog.pg_get_keywords() WHERE catcode = 'R' ORDER BY 1;
+-------------------+
| word              |
+-------------------+
| add               |
| all               |
| alter             |
| and               |
| any               |
| array             |
| as                |
| asc               |
| between           |
| by                |
| called            |
| case              |
| cast              |
| column            |
| constraint        |
| create            |
| cross             |
| current_date      |
| current_schema    |
| current_time      |
| current_timestamp |
| current_user      |
| default           |
| delete            |
| deny              |
| desc              |
| describe          |
| directory         |
| distinct          |
| drop              |
| else              |
| end               |
| escape            |
| except            |
| exists            |
| extract           |
| false             |
| first             |
| for               |
| from              |
| full              |
| function          |
| grant             |
| group             |
| having            |
| if                |
| in                |
| index             |
| inner             |
| input             |
| insert            |
| intersect         |
| into              |
| is                |
| join              |
| last              |
| left              |
| like              |
| limit             |
| match             |
| natural           |
| not               |
| null              |
| nulls             |
| object            |
| offset            |
| on                |
| or                |
| order             |
| outer             |
| persistent        |
| recursive         |
| reset             |
| returns           |
| revoke            |
| right             |
| select            |
| session_user      |
| set               |
| some              |
| stratify          |
| substring         |
| table             |
| then              |
| transient         |
| true              |
| try_cast          |
| unbounded         |
| union             |
| update            |
| user              |
| using             |
| when              |
| where             |
| with              |
+-------------------+
SELECT 95 rows in set (... sec)

Tokens such as my_table, id, name, or data in the example below are identifiers, which identify names of tables, columns, and other database objects.

Example:

CREATE TABLE my_table (
  id INTEGER,
  name STRING,
  data OBJECT
) WITH (number_of_replicas = 0);

Note

Key words and unquoted identifiers are case insensitive.

This means that:

select foo from t;

is equivalent to:

select Foo from t;

or:

select FOO from t;

A widely used convention is to write key words in uppercase and identifiers in lowercase, such as

ALTER TABLE foo ADD COLUMN new_column INTEGER;

INSERT INTO foo (id, name) VALUES (1, 'bar');

Quoted identifiers can contain an arbitrary sequence of characters enclosed by double quotes ("). Quoted identifiers are never keywords, so you can use "update" as a table or column name.

Special characters

Some non-alphanumeric characters do have a special meaning. For their usage please refer to the sections where the respective syntax elements are described.

Semicolon

The semicolon (;) terminates an SQL statement. It cannot appear anywhere else within the command, except within a string or quoted identifier.

Comma

The comma (,) is used in various syntactical elements to separate elements of a list.

Brackets

Square brackets ([]) are used to select elements of arrays and objects, e.g. arr[1] or obj['key'].

Asterisk

The asterisk (*) is used in some contexts to denote all columns of a table. As an argument in global aggregate functions it has the meaning of any field, e.g. COUNT(*).

Period

The period (.) is used for numeric values and to separate schema and table names, e.g. blob.my_blob_table.

Comments

An SQL statement can contain comments. Single line comments start with a double dash (--) and end at the end of that line. Multi line comments start with /* and end with */.

Example:

/*
 * Retrieve information about all tables in the 'doc' schema.
 */
SELECT *
  FROM information_schema.tables
  WHERE table_schema = 'doc'; -- query information schema for doc tables