查询以在多个表上的字段上计算不同不工作

Question

SQL 查询：

Select count(distinct signature)
from (Select table_name
      from information_schema.tables
      where table_schema="Log" and table_name like "%ERROR_%")
AS mytable;

预期输出： 所有表中不同 "Signature" 的数量。

实际输出： 'field list' 中的未知列 'signature'；

注意：我所有的表都有签名作为字段名

Answer 1

嗯，你的子查询是这样开始的：

Select table_name from information_schema.tables

所以您要拉入的可用列是 "table_name"。

因此，如果您尝试 select 来自该子查询的签名，它会告诉您没有这样的列。

你可能想做这样的事情（伪代码）：

query(
    Select table_name 
    from information_schema.tables 
    where table_schema="Log" and table_name like "%ERROR_%"
)
$sql = '';
$sep = '';
while ($row = fetch_assoc()) {
    $sql .= $sep."SELECT signature FROM $row[table_name] ";
    $sep = 'UNION ALL ';
}
$sql = "SELECT COUNT(DISTINCT signature) as c FROM ($sql)";
query($sql);
$row = fetch_assoc()
echo "There are $row[c] distinct signatures.<br />\n";

Answer 2

您似乎在 mysql 端尝试动态查询。请检查这个...

-- Step1. prepare your select query here
set @sqlQuery := 
(select
 GROUP_CONCAT(
  concat(' SELECT \'',table_name,'\' as col1,  COUNT(*) as countItem FROM ', table_name)
  SEPARATOR ' UNION ALL '
)  from information_schema.tables as t
where t.table_schema="Log" and t.table_name like "%ERROR_%");

-- Step2. execute the dynamic query
prepare stmt from @sqlQuery;
execute stmt;
drop prepare stmt;

查询以在多个表上的字段上计算不同不工作

Query to count distict on a field on multiple tables not working

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