有没有办法从相同的以下查询中选择行数？

Question

我能否将行数添加到同一个查询中，还是需要单独创建一个？

SELECT DISTINCT c.TABLE_SCHEMA, c.TABLE_NAME, c.COLUMN_NAME, c.DATA_TYPE, \
                ( \
                    SELECT DISTINCT p.CONSTRAINT_TYPE \
                    FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu \
                        INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS p ON p.CONSTRAINT_NAME=kcu.CONSTRAINT_NAME AND p.CONSTRAINT_TYPE=\'PRIMARY KEY\' \
                    WHERE kcu.TABLE_NAME = c.TABLE_NAME AND kcu.COLUMN_NAME=c.COLUMN_NAME \
                ) AS CONSTRAINT_TYPE, NULL AS DATA_PRECISION, NULL AS DATA_SCALE \
                FROM INFORMATION_SCHEMA.COLUMNS c 

Answer 1

你可以用cte做到这一点

    with cte as
    (
    SELECT DISTINCT c.TABLE_SCHEMA, c.TABLE_NAME, c.COLUMN_NAME, c.DATA_TYPE, 
                    ( 
                        SELECT DISTINCT p.CONSTRAINT_TYPE 
                        FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu 
                            INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS p ON p.CONSTRAINT_NAME=kcu.CONSTRAINT_NAME AND p.CONSTRAINT_TYPE='PRIMARY KEY' 
                        WHERE kcu.TABLE_NAME = c.TABLE_NAME AND kcu.COLUMN_NAME=c.COLUMN_NAME 
                    ) AS CONSTRAINT_TYPE, NULL AS DATA_PRECISION, NULL AS DATA_SCALE 
                    FROM INFORMATION_SCHEMA.COLUMNS c 
    )
select *, (select count(*) from cte)  as  _Count
from
cte 

Answer 2

通常，如果不需要相关子查询并且您不支持window functions，则应避免在SELECT 中运行子查询（在MySQL 8+ 中可用）。因此，将子查询移动到JOIN 作为派生表并合并行计数只需运行JOIN INFORMATION_SCHEMA.TABLES：

SELECT DISTINCT c.TABLE_SCHEMA, c.TABLE_NAME, c.COLUMN_NAME, c.DATA_TYPE, 
                t.CONSTRAINT_TYPE, NULL AS DATA_PRECISION, 
                NULL AS DATA_SCALE, r.TABLE_ROWS     

FROM INFORMATION_SCHEMA.COLUMNS c

INNER JOIN (
   SELECT DISTINCT kcu.TABLE_NAME, kcu.COLUMN_NAME, p.CONSTRAINT_TYPE
   FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu
   INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS p
       ON p.CONSTRAINT_NAME = kcu.CONSTRAINT_NAME
      AND p.CONSTRAINT_TYPE = \'PRIMARY KEY\'
  ) AS t
  ON t.TABLE_NAME = c.TABLE_NAME 
  AND t.COLUMN_NAME = c.COLUMN_NAME

INNER JOIN INFORMATION_SCHEMA.TABLES r
  ON r.TABLE_NAME = c.TABLE_NAME 
  AND r.TABLE_SCHEMA = c.TABLE_SCHEMA

Answer 3

SELECT DISTINCT c.TABLE_SCHEMA, 
                c.TABLE_NAME, 
                c.COLUMN_NAME, 
                c.DATA_TYPE, 
                ( SELECT DISTINCT p.CONSTRAINT_TYPE 
                  FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu 
                  INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS p 
                       ON p.CONSTRAINT_NAME=kcu.CONSTRAINT_NAME 
                      AND p.CONSTRAINT_TYPE='PRIMARY KEY' 
                  WHERE kcu.TABLE_NAME = c.TABLE_NAME 
                    AND kcu.COLUMN_NAME=c.COLUMN_NAME ) AS CONSTRAINT_TYPE, 
                NULL AS DATA_PRECISION, 
                NULL AS DATA_SCALE,

                COUNT(*) OVER () total_records_count 

FROM INFORMATION_SCHEMA.COLUMNS c