SQL 将一列拆分成多列的实现示例

目录

• 需求一：将col列拆分成三列
• 假设想把 "col" 列分成 "col1" 、 "col2"、 "col3"，SQL语句：
• 需求二：列col保存的数据，是字典表dictionary中id值拼接的字符串，想关联出对应 的name值。
• 需求三：列col转化为字典表dictionary中name拼接的字符串
• 总结 ：

SELECT col,a[1] a1,a[2] a2,a[3] a3
FROM
    ( 
        SELECT regexp_split_to_array( col, ',' ), col FROM t1 
    ) AS dt (a)

SELECT
    col,
    SPLIT_PART( col, ',', 1 ) a1,
    SPLIT_PART( col, ',', 2 ) a2,
    SPLIT_PART( col, ',', 3 ) a3 
FROM
    t1

ALTER TABLE t1 ADD COLUMN col1 VARCHAR(30);
ALTER TABLE t1 ADD COLUMN col2 VARCHAR(30);
ALTER TABLE t1 ADD COLUMN col3 VARCHAR(30);

UPDATE t1 
SET col1 = SPLIT_PART( col, ',', 1 ),
col2 = SPLIT_PART( col, ',', 2 ),
col3 = SPLIT_PART( col, ',', 3 );

SELECT col,
    (SELECT name from dictionary WHERE id=a[1]) a1,
    (SELECT name from dictionary WHERE id=a[2]) a2,
    (SELECT name from dictionary WHERE id=a[3]) a3
FROM
    ( 
        SELECT regexp_split_to_array( col, ',' ), col FROM t1 
    ) AS dt (a)

SELECT col,CONCAT_WS(',',a1,a2,a3) as names
FROM
    ( 
        SELECT col,
            (SELECT name from dictionary WHERE id=a[1]) a1,
            (SELECT name from dictionary WHERE id=a[2]) a2,
            (SELECT name from dictionary WHERE id=a[3]) a3
        FROM
            ( 
                SELECT regexp_split_to_array( col, ',' ), col FROM t1 
            ) AS dt (a)
    ) as temp

SELECT max(array_length(regexp_split_to_array(col,','),1))