Query syntax

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Query statements scan one or more tables or expressions and return the computed result rows. This topic describes the syntax for SQL queries in GoogleSQL for BigQuery.

SQL syntax notation rules

The GoogleSQL documentation commonly uses the following syntax notation rules:

• Square brackets [ ]: Optional clause.
• Curly braces with vertical bars { a | b | c }: Logical OR. Select one option.
• Ellipsis ...: Preceding item can repeat.
• Red square brackets [ ]: Required and part of the syntax.
• Red curly braces { }: Required and part of the syntax.
• Red vertical bar |: Required and part of the syntax.

SQL syntax

query_statement:
    query_expr

query_expr:
  [ WITH [ RECURSIVE ] { non_recursive_cte | recursive_cte }[, ...] ]
  { select | ( query_expr ) | set_operation }
  [ ORDER BY expression [{ ASC | DESC }] [, ...] ]
  [ LIMIT count [ OFFSET skip_rows ] ]

select:
  SELECT
    [ WITH differential_privacy_clause ]
    [ { ALL | DISTINCT } ]
    [ AS { STRUCT | VALUE } ]
    select_list
  [ FROM from_clause[, ...] ]
  [ WHERE bool_expression ]
  [ GROUP BY group_by_specification ]
  [ HAVING bool_expression ]
  [ QUALIFY bool_expression ]
  [ WINDOW window_clause ]

SELECT statement

SELECT
  [ WITH differential_privacy_clause ]
  [ { ALL | DISTINCT } ]
  [ AS { STRUCT | VALUE } ]
  select_list

select_list:
  { select_all | select_expression } [, ...]

select_all:
  [ expression. ]*
  [ EXCEPT ( column_name [, ...] ) ]
  [ REPLACE ( expression [ AS ] column_name [, ...] ) ]

select_expression:
  expression [ [ AS ] alias ]

The SELECT list defines the columns that the query will return. Expressions in the SELECT list can refer to columns in any of the from_items in its corresponding FROM clause.

Each item in the SELECT list is one of:

• *
• expression
• expression.*

SELECT *

SELECT *, often referred to as select star, produces one output column for each column that is visible after executing the full query.

SELECT * FROM (SELECT "apple" AS fruit, "carrot" AS vegetable);

/*-------+-----------*
 | fruit | vegetable |
 +-------+-----------+
 | apple | carrot    |
 *-------+-----------*/

SELECT expression

Items in a SELECT list can be expressions. These expressions evaluate to a single value and produce one output column, with an optional explicit alias.

If the expression doesn't have an explicit alias, it receives an implicit alias according to the rules for implicit aliases, if possible. Otherwise, the column is anonymous and you cannot refer to it by name elsewhere in the query.

SELECT expression.*

An item in a SELECT list can also take the form of expression.*. This produces one output column for each column or top-level field of expression. The expression must either be a table alias or evaluate to a single value of a data type with fields, such as a STRUCT.

The following query produces one output column for each column in the table groceries, aliased as g.

WITH groceries AS
  (SELECT "milk" AS dairy,
   "eggs" AS protein,
   "bread" AS grain)
SELECT g.*
FROM groceries AS g;

/*-------+---------+-------*
 | dairy | protein | grain |
 +-------+---------+-------+
 | milk  | eggs    | bread |
 *-------+---------+-------*/

More examples:

WITH locations AS
  (SELECT STRUCT("Seattle" AS city, "Washington" AS state) AS location
  UNION ALL
  SELECT STRUCT("Phoenix" AS city, "Arizona" AS state) AS location)
SELECT l.location.*
FROM locations l;

/*---------+------------*
 | city    | state      |
 +---------+------------+
 | Seattle | Washington |
 | Phoenix | Arizona    |
 *---------+------------*/

WITH locations AS
  (SELECT ARRAY<STRUCT<city STRING, state STRING>>[("Seattle", "Washington"),
    ("Phoenix", "Arizona")] AS location)
SELECT l.LOCATION[offset(0)].*
FROM locations l;

/*---------+------------*
 | city    | state      |
 +---------+------------+
 | Seattle | Washington |
 *---------+------------*/

SELECT * EXCEPT

A SELECT * EXCEPT statement specifies the names of one or more columns to exclude from the result. All matching column names are omitted from the output.

WITH orders AS
  (SELECT 5 as order_id,
  "sprocket" as item_name,
  200 as quantity)
SELECT * EXCEPT (order_id)
FROM orders;

/*-----------+----------*
 | item_name | quantity |
 +-----------+----------+
 | sprocket  | 200      |
 *-----------+----------*/

Note: SELECT * EXCEPT doesn't exclude columns that don't have names.

SELECT * REPLACE

A SELECT * REPLACE statement specifies one or more expression AS identifier clauses. Each identifier must match a column name from the SELECT * statement. In the output column list, the column that matches the identifier in a REPLACE clause is replaced by the expression in that REPLACE clause.

A SELECT * REPLACE statement doesn't change the names or order of columns. However, it can change the value and the value type.

WITH orders AS
  (SELECT 5 as order_id,
  "sprocket" as item_name,
  200 as quantity)
SELECT * REPLACE ("widget" AS item_name)
FROM orders;

/*----------+-----------+----------*
 | order_id | item_name | quantity |
 +----------+-----------+----------+
 | 5        | widget    | 200      |
 *----------+-----------+----------*/

WITH orders AS
  (SELECT 5 as order_id,
  "sprocket" as item_name,
  200 as quantity)
SELECT * REPLACE (quantity/2 AS quantity)
FROM orders;

/*----------+-----------+----------*
 | order_id | item_name | quantity |
 +----------+-----------+----------+
 | 5        | sprocket  | 100      |
 *----------+-----------+----------*/

Note: SELECT * REPLACE doesn't replace columns that don't have names.

SELECT DISTINCT

A SELECT DISTINCT statement discards duplicate rows and returns only the remaining rows. SELECT DISTINCT cannot return columns of the following types:

• STRUCT
• ARRAY

SELECT ALL

A SELECT ALL statement returns all rows, including duplicate rows. SELECT ALL is the default behavior of SELECT.

SELECT AS STRUCT

SELECT AS STRUCT expr [[AS] struct_field_name1] [,...]

This produces a value table with a STRUCT row type, where the STRUCT field names and types match the column names and types produced in the SELECT list.

Example:

SELECT ARRAY(SELECT AS STRUCT 1 a, 2 b)

SELECT AS STRUCT can be used in a scalar or array subquery to produce a single STRUCT type grouping multiple values together. Scalar and array subqueries (see Subqueries) are normally not allowed to return multiple columns, but can return a single column with STRUCT type.

SELECT AS VALUE

SELECT AS VALUE produces a value table from any SELECT list that produces exactly one column. Instead of producing an output table with one column, possibly with a name, the output will be a value table where the row type is just the value type that was produced in the one SELECT column. Any alias the column had will be discarded in the value table.

Example:

SELECT AS VALUE STRUCT(1 AS a, 2 AS b) xyz

The query above produces a table with row type STRUCT<a int64, b int64>.

FROM clause

FROM from_clause[, ...]

from_clause:
  from_item
  [ { pivot_operator | unpivot_operator } ]
  [ tablesample_operator ]

from_item:
  {
    table_name [ as_alias ] [ FOR SYSTEM_TIME AS OF timestamp_expression ] 
    | { join_operation | ( join_operation ) }
    | ( query_expr ) [ as_alias ]
    | field_path
    | unnest_operator
    | cte_name [ as_alias ]
  }

as_alias:
  [ AS ] alias

The FROM clause indicates the table or tables from which to retrieve rows, and specifies how to join those rows together to produce a single stream of rows for processing in the rest of the query.

pivot_operator

See PIVOT operator.

unpivot_operator

See UNPIVOT operator.

tablesample_operator

See TABLESAMPLE operator.

table_name

The name (optionally qualified) of an existing table.

SELECT * FROM Roster;
SELECT * FROM dataset.Roster;
SELECT * FROM project.dataset.Roster;

FOR SYSTEM_TIME AS OF

FOR SYSTEM_TIME AS OF references the historical versions of the table definition and rows that were current at timestamp_expression.

Limitations:

The source table in the FROM clause containing FOR SYSTEM_TIME AS OF must not be any of the following:

• An array scan, including a flattened array or the output of the UNNEST operator.
• A common table expression defined by a WITH clause.

timestamp_expression must be a constant expression. It cannot contain the following:

• Subqueries.
• Correlated references (references to columns of a table that appear at a higher level of the query statement, such as in the SELECT list).
• User-defined functions (UDFs).

The value of timestamp_expression cannot fall into the following ranges:

• After the current timestamp (in the future).
• More than seven (7) days before the current timestamp.

A single query statement cannot reference a single table at more than one point in time, including the current time. That is, a query can reference a table multiple times at the same timestamp, but not the current version and a historical version, or two different historical versions.

Note: DML statements always operate on the current version of the destination table, so if the destination table is used multiple times in the query, all of them must use the current version.

The default time zone for timestamp_expression in a FOR SYSTEM_TIME AS OF expression is America/Los_Angeles, even though the default time zone for timestamp literals is UTC.

Examples:

The following query returns a historical version of the table from one hour ago.

SELECT *
FROM t
  FOR SYSTEM_TIME AS OF TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 1 HOUR);

The following query returns a historical version of the table at an absolute point in time.

SELECT *
FROM t
  FOR SYSTEM_TIME AS OF '2017-01-01 10:00:00-07:00';

The following query returns an error because the timestamp_expression contains a correlated reference to a column in the containing query.

SELECT *
FROM t1
WHERE t1.a IN (SELECT t2.a
               FROM t2 FOR SYSTEM_TIME AS OF t1.timestamp_column);

The following operations show accessing a historical version of the table before table is replaced.

DECLARE before_replace_timestamp TIMESTAMP;

-- Create table books.
CREATE TABLE books AS
SELECT 'Hamlet' title, 'William Shakespeare' author;

-- Get current timestamp before table replacement.
SET before_replace_timestamp = CURRENT_TIMESTAMP();

-- Replace table with different schema(title and release_date).
CREATE OR REPLACE TABLE books AS
SELECT 'Hamlet' title, DATE '1603-01-01' release_date;

-- This query returns Hamlet, William Shakespeare as result.
SELECT * FROM books FOR SYSTEM_TIME AS OF before_replace_timestamp;

The following operations show accessing a historical version of the table before a DML job.

DECLARE JOB_START_TIMESTAMP TIMESTAMP;

-- Create table books.
CREATE OR REPLACE TABLE books AS
SELECT 'Hamlet' title, 'William Shakespeare' author;

-- Insert two rows into the books.
INSERT books (title, author)
VALUES('The Great Gatsby', 'F. Scott Fizgerald'),
      ('War and Peace', 'Leo Tolstoy');

SELECT * FROM books;

SET JOB_START_TIMESTAMP = (
  SELECT start_time
  FROM `region-us`.INFORMATION_SCHEMA.JOBS_BY_USER
  WHERE job_type="QUERY"
    AND statement_type="INSERT"
  ORDER BY start_time DESC
  LIMIT 1
 );

-- This query only returns Hamlet, William Shakespeare as result.
SELECT * FROM books FOR SYSTEM_TIME AS OF JOB_START_TIMESTAMP;

The following query returns an error because the DML operates on the current version of the table, and a historical version of the table from one day ago.

INSERT INTO t1
SELECT * FROM t1
  FOR SYSTEM_TIME AS OF TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 1 DAY);

join_operation

See Join operation.

query_expr

( query_expr ) [ [ AS ] alias ] is a table subquery.

field_path

In the FROM clause, field_path is any path that resolves to a field within a data type. field_path can go arbitrarily deep into a nested data structure.

Some examples of valid field_path values include:

SELECT * FROM T1 t1, t1.array_column;

SELECT * FROM T1 t1, t1.struct_column.array_field;

SELECT (SELECT ARRAY_AGG(c) FROM t1.array_column c) FROM T1 t1;

SELECT a.struct_field1 FROM T1 t1, t1.array_of_structs a;

SELECT (SELECT STRING_AGG(a.struct_field1) FROM t1.array_of_structs a) FROM T1 t1;

Field paths in the FROM clause must end in an array field. In addition, field paths cannot contain arrays before the end of the path. For example, the path array_column.some_array.some_array_field is invalid because it contains an array before the end of the path.

Note: If a path has only one name, it is interpreted as a table. To work around this, wrap the path using UNNEST, or use the fully-qualified path.

Note: If a path has more than one name, and it matches a field name, it is interpreted as a field name. To force the path to be interpreted as a table name, wrap the path using `.

unnest_operator

See UNNEST operator.

cte_name

Common table expressions (CTEs) in a WITH Clause act like temporary tables that you can reference anywhere in the FROM clause. In the example below, subQ1 and subQ2 are CTEs.

Example:

WITH
  subQ1 AS (SELECT * FROM Roster WHERE SchoolID = 52),
  subQ2 AS (SELECT SchoolID FROM subQ1)
SELECT DISTINCT * FROM subQ2;

The WITH clause hides any permanent tables with the same name for the duration of the query, unless you qualify the table name, for example:

dataset.Roster or project.dataset.Roster.

UNNEST operator

unnest_operator:
  {
    UNNEST( array_expression )
    | UNNEST( array_path )
    | array_path
  }
  [ as_alias ]
  [ WITH OFFSET [ as_alias ] ]

as_alias:
  [AS] alias

The UNNEST operator takes an array and returns a table, with one row for each element in the array. For input arrays of most element types, the output of UNNEST generally has one column. ARRAYS with these element types return multiple columns:

• STRUCT
• JSON

Input values:

• array_expression: An expression that produces an array.
• table_name: The name of a table.

• array_path: The path to an ARRAY type.array_path must be prepended with a table in an implicit UNNEST operation, but otherwise is optional.

  The UNNEST operation with a correlated array_path must be on the right side of a CROSS JOIN, LEFT JOIN, or INNER JOIN operation.

• WITH OFFSET: UNNEST destroys the order of elements in the input array. Use this optional clause to return an additional column with the array element indexes, or offsets. Offset counting starts at zero for each row produced by the UNNEST operation. This column has an optional alias; If the optional alias is not used, the default column name is offset.

  Example:

  SELECT * FROM UNNEST ([10,20,30]) as numbers WITH OFFSET;
  
  /*---------+--------*
   | numbers | offset |
   +---------+--------+
   | 10      | 0      |
   | 20      | 1      |
   | 30      | 2      |
   *---------+--------*/
  

• alias: An alias for a value table. An input array that produces a single column can have an optional alias, which you can use to refer to the column elsewhere in the query. You can also use an additional alias with the WITH OFFSET clause to rename the offset column.

You can also use UNNEST outside of the FROM clause with the IN operator.

For several ways to use UNNEST, including construction, flattening, and filtering, see Work with arrays.

To learn more about the ways you can use UNNEST explicitly and implicitly, see Explicit and implicit UNNEST.

UNNEST and structs

For an input array of structs, UNNEST returns a row for each struct, with a separate column for each field in the struct. The alias for each column is the name of the corresponding struct field.

Example:

SELECT *
FROM UNNEST(
  ARRAY<
    STRUCT<
      x INT64,
      y STRING,
      z STRUCT<a INT64, b INT64>>>[
        (1, 'foo', (10, 11)),
        (3, 'bar', (20, 21))]);

/*---+-----+----------*
 | x | y   | z        |
 +---+-----+----------+
 | 1 | foo | {10, 11} |
 | 3 | bar | {20, 21} |
 *---+-----+----------*/

Because the UNNEST operator returns a value table, you can alias UNNEST to define a range variable that you can reference elsewhere in the query. If you reference the range variable in the SELECT list, the query returns a struct containing all of the fields of the original struct in the input table.

Example:

SELECT *, struct_value
FROM UNNEST(
  ARRAY<
    STRUCT<
    x INT64,
    y STRING>>[
      (1, 'foo'),
      (3, 'bar')]) AS struct_value;

/*---+-----+--------------*
 | x | y   | struct_value |
 +---+-----+--------------+
 | 3 | bar | {3, bar}     |
 | 1 | foo | {1, foo}     |
 *---+-----+--------------*/

Explicit and implicit UNNEST

Array unnesting can be either explicit or implicit. To learn more, see the following sections.

Explicit unnesting

The UNNEST keyword is required in explicit unnesting. For example:

WITH Coordinates AS (SELECT [1,2] AS position)
SELECT results FROM Coordinates, UNNEST(Coordinates.position) AS results;

In explicit unnesting, array_expression must return an array value but doesn't need to resolve to an array.

Implicit unnesting

The UNNEST keyword is not used in implicit unnesting.

For example:

WITH Coordinates AS (SELECT [1,2] AS position)
SELECT results FROM Coordinates, Coordinates.position AS results;

Tables and implicit unnesting

When you use array_path with implicit UNNEST, array_path must be prepended with the table. For example:

WITH Coordinates AS (SELECT [1,2] AS position)
SELECT results FROM Coordinates, Coordinates.position AS results;

UNNEST and NULL values

UNNEST treats NULL values as follows:

• NULL and empty arrays produce zero rows.
• An array containing NULL values produces rows containing NULL values.

PIVOT operator

FROM from_item[, ...] pivot_operator

pivot_operator:
  PIVOT(
    aggregate_function_call [as_alias][, ...]
    FOR input_column
    IN ( pivot_column [as_alias][, ...] )
  ) [AS alias]

as_alias:
  [AS] alias

The PIVOT operator rotates rows into columns, using aggregation. PIVOT is part of the FROM clause.

• PIVOT can be used to modify any table expression.
• Combining PIVOT with FOR SYSTEM_TIME AS OF is not allowed, although users may use PIVOT against a subquery input which itself uses FOR SYSTEM_TIME AS OF.
• A WITH OFFSET clause immediately preceding the PIVOT operator is not allowed.

Conceptual example:

-- Before PIVOT is used to rotate sales and quarter into Q1, Q2, Q3, Q4 columns:
/*---------+-------+---------+------*
 | product | sales | quarter | year |
 +---------+-------+---------+------|
 | Kale    | 51    | Q1      | 2020 |
 | Kale    | 23    | Q2      | 2020 |
 | Kale    | 45    | Q3      | 2020 |
 | Kale    | 3     | Q4      | 2020 |
 | Kale    | 70    | Q1      | 2021 |
 | Kale    | 85    | Q2      | 2021 |
 | Apple   | 77    | Q1      | 2020 |
 | Apple   | 0     | Q2      | 2020 |
 | Apple   | 1     | Q1      | 2021 |
 *---------+-------+---------+------*/

-- After PIVOT is used to rotate sales and quarter into Q1, Q2, Q3, Q4 columns:
/*---------+------+----+------+------+------*
 | product | year | Q1 | Q2   | Q3   | Q4   |
 +---------+------+----+------+------+------+
 | Apple   | 2020 | 77 | 0    | NULL | NULL |
 | Apple   | 2021 | 1  | NULL