JOIN

適用於： Databricks SQL Databricks Runtime

根據聯結準則，結合兩 個數據表參考 中的數據列。

語法

left_table_reference { [ join_type ] JOIN right_table_reference join_criteria |
           NATURAL join_type JOIN right_table_reference |
           CROSS JOIN right_table_reference }

join_type
  { [ INNER ] |
    LEFT [ OUTER ] |
    [ LEFT ] SEMI |
    RIGHT [ OUTER ] |
    FULL [ OUTER ] |
    [ LEFT ] ANTI |
    CROSS }

join_criteria
  { ON boolean_expression |
    USING ( column_name [, ...] ) }

參數

• left_table_reference

  聯結左側的數據表參考。

• right_table_reference

  聯結右側的數據表參考。

• join_type

  聯結類型。

  • [ INNER ]

    傳回在這兩個數據表參考中具有相符值的數據列。 默認聯結類型。

  • LEFT [ OUTER ]

    從左資料表參考傳回所有值，以及來自右資料表參考的相符值，如果沒有相符專案，則會附加 NULL 。 也稱為 左外部聯接。

  • RIGHT [ OUTER ]

    從右資料表參考傳回所有值，以及來自左資料表參考的相符值，如果沒有相符專案，則會附加 NULL 。 也稱為 右外部聯接。

  • FULL [OUTER]

    傳回這兩個關聯中的所有值，並將 NULL 值附加在不相符的一邊。 也稱為 完整外部聯接。

  • [ LEFT ]半

    從數據表參考左側傳回值，該參考與右邊相符。 也稱為 左半聯結。

  • [ LEFT ]反

    從左數據表參考傳回與右數據表參考沒有相符的值。 也稱為 左反聯結。

• CROSS JOIN

  傳回兩個關聯性之笛卡兒乘積。

• NATURAL

  指定兩個關聯性中的數據列會以相等方式隱含地比對具有相符名稱的所有數據行。

• join_criteria

  指定一個數據表參考中的數據列如何與另一個數據表參考的數據列結合。

  • ON boolean_expression

    具有 BOOLEAN 傳回型別的運算式，指定兩個關聯數據列的比對方式。 如果結果為 true，則會將數據列視為相符專案。

  • USING （ column_name [， ...] ）

    比較兩個關聯中必須存在之數據行清單 column_name 的相等性，以比對數據列。

• table_alias

  具有選擇性數據行標識碼清單的暫存名稱。

備註

當您指定 USING 或 NATURAL時， SELECT * 只會針對每個用來比對的數據行顯示一個相符專案，後面接著左邊的數據行，然後是右聯結數據表，排除所聯結的數據行。

SELECT * FROM left JOIN right USING (a, b)

相當於

SELECT left.a, left.b,
       left.* EXCEPT(a, b),
       right.* EXCEPT(a, b)
  FROM left JOIN right ON left.a = right.a AND left.b = right.b

如果您省略 join_criteria 任何 join_type 的語意會變成 的語 CROSS JOIN意。

範例

-- Use employee and department tables to demonstrate different type of joins.
> CREATE TEMP VIEW employee(id, name, deptno) AS
     VALUES(105, 'Chloe', 5),
           (103, 'Paul' , 3),
           (101, 'John' , 1),
           (102, 'Lisa' , 2),
           (104, 'Evan' , 4),
           (106, 'Amy'  , 6);

> CREATE TEMP VIEW department(deptno, deptname) AS
    VALUES(3, 'Engineering'),
          (2, 'Sales'      ),
          (1, 'Marketing'  );

-- Use employee and department tables to demonstrate inner join.
> SELECT id, name, employee.deptno, deptname
   FROM employee
   INNER JOIN department ON employee.deptno = department.deptno;
 103  Paul      3 Engineering
 101  John      1   Marketing
 102  Lisa      2       Sales

-- Use employee and department tables to demonstrate left join.
> SELECT id, name, employee.deptno, deptname
   FROM employee
   LEFT JOIN department ON employee.deptno = department.deptno;
 105 Chloe      5        NULL
 103  Paul      3 Engineering
 101  John      1   Marketing
 102  Lisa      2       Sales
 104  Evan      4        NULL
 106   Amy      6        NULL

-- Use employee and department tables to demonstrate right join.
> SELECT id, name, employee.deptno, deptname
    FROM employee
    RIGHT JOIN department ON employee.deptno = department.deptno;
 103  Paul      3 Engineering
 101  John      1   Marketing
 102  Lisa      2       Sales

-- Use employee and department tables to demonstrate full join.
> SELECT id, name, employee.deptno, deptname
    FROM employee
    FULL JOIN department ON employee.deptno = department.deptno;
 101  John      1   Marketing
 106   Amy      6        NULL
 103  Paul      3 Engineering
 105 Chloe      5        NULL
 104  Evan      4        NULL
 102  Lisa      2       Sales

-- Use employee and department tables to demonstrate cross join.
> SELECT id, name, employee.deptno, deptname
    FROM employee
    CROSS JOIN department;
 105 Chloe      5 Engineering
 105 Chloe      5   Marketing
 105 Chloe      5       Sales
 103  Paul      3 Engineering
 103  Paul      3   Marketing
 103  Paul      3       Sales
 101  John      1 Engineering
 101  John      1   Marketing
 101  John      1       Sales
 102  Lisa      2 Engineering
 102  Lisa      2   Marketing
 102  Lisa      2       Sales
 104  Evan      4 Engineering
 104  Evan      4   Marketing
 104  Evan      4       Sales
 106   Amy      4 Engineering
 106   Amy      4   Marketing
 106   Amy      4       Sales

-- Use employee and department tables to demonstrate semi join.
> SELECT *
    FROM employee
    SEMI JOIN department ON employee.deptno = department.deptno;
 103  Paul      3
 101  John      1
 102  Lisa      2

-- Use employee and department tables to demonstrate anti join.
> SELECT *
    FROM employee
    ANTI JOIN department ON employee.deptno = department.deptno;
 105 Chloe      5
 104  Evan      4
 106   Amy      6

-- Use employee and department tables to demonstrate lateral inner join.
> SELECT id, name, deptno, deptname
    FROM employee
    JOIN LATERAL (SELECT deptname
                    FROM department
                    WHERE employee.deptno = department.deptno);
 103 Paul    3  Engineering
 101 John    1  Marketing
 102 Lisa    2  Sales

-- Use employee and department tables to demonstrate lateral left join.
> SELECT id, name, deptno, deptname
    FROM employee
    LEFT JOIN LATERAL (SELECT deptname
                         FROM department
                         WHERE employee.deptno = department.deptno);
 105 Chloe   5      NULL
 103 Paul    3      Engineering
 101 John    1      Marketing
 102 Lisa    2      Sales
 104 Evan    4      NULL
 106 Amy     6      NULL

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