Ortak tablo ifadesi (CTE)

Bir SQL ifadesinin kapsamı içinde muhtemelen birden çok kez başvurabileceğini sağlayan geçici bir sonuç kümesi tanımlar. Bir CTE, temel olarak bir SELECT ifadede kullanılır.

Syntax

WITH common_table_expression [ , ... ]

common_table_expressionŞöyle tanımlanır

expression_name [ ( column_name [ , ... ] ) ] [ AS ] ( query )

Parametreler

  • expression_name

    Ortak tablo ifadesi için bir ad.

  • sorgulayamadı

    Bir SELECT deyimidir.

Örnekler

-- CTE with multiple column aliases
WITH t(x, y) AS (SELECT 1, 2)
SELECT * FROM t WHERE x = 1 AND y = 2;
+---+---+
|  x|  y|
+---+---+
|  1|  2|
+---+---+

-- CTE in CTE definition
WITH t AS (
    WITH t2 AS (SELECT 1)
    SELECT * FROM t2
)
SELECT * FROM t;
+---+
|  1|
+---+
|  1|
+---+

-- CTE in subquery
SELECT max(c) FROM (
    WITH t(c) AS (SELECT 1)
    SELECT * FROM t
);
+------+
|max(c)|
+------+
|     1|
+------+

-- CTE in subquery expression
SELECT (
    WITH t AS (SELECT 1)
    SELECT * FROM t
);
+----------------+
|scalarsubquery()|
+----------------+
|               1|
+----------------+

-- CTE in CREATE VIEW statement
CREATE VIEW v AS
    WITH t(a, b, c, d) AS (SELECT 1, 2, 3, 4)
    SELECT * FROM t;
SELECT * FROM v;
+---+---+---+---+
|  a|  b|  c|  d|
+---+---+---+---+
|  1|  2|  3|  4|
+---+---+---+---+

-- If name conflict is detected in nested CTE, then AnalysisException is thrown by default.
-- SET spark.sql.legacy.ctePrecedencePolicy = CORRECTED (which is recommended),
-- inner CTE definitions take precedence over outer definitions.
SET spark.sql.legacy.ctePrecedencePolicy = CORRECTED;
WITH
    t AS (SELECT 1),
    t2 AS (
        WITH t AS (SELECT 2)
        SELECT * FROM t
    )
SELECT * FROM t2;
+---+
|  2|
+---+
|  2|
+---+