SQL Server 中的 IF 子句或 CASE 语句答案

【问题标题】：IF clause or CASE statement in SQL ServerSQL Server 中的 IF 子句或 CASE 语句
【发布时间】：2011-06-27 19:25:10
【问题描述】：

我该如何执行以下代码：

 SELECT c.TABLE_NAME, c.COLUMN_NAME, c.DATA_TYPE, c.Column_default, c.character_maximum_length, c.numeric_precision, c.is_nullable,
 if(u.CONSTRAINT_TYPE = 'PRIMARY KEY')
 Begin
print 'primary key'
 end
else
begin
print ''
end
 FROM INFORMATION_SCHEMA.COLUMNS as c
 LEFT OUTER JOIN information_schema.CONSTRAINT_table_USAGE as u
 ON c.table_name = u.table_name
 Order by table_name

【问题讨论】：

标签： sql-server if-statement case

【解决方案1】：

SELECT
    c.TABLE_NAME, c.COLUMN_NAME, c.DATA_TYPE, c.Column_default,
    c.character_maximum_length, c.numeric_precision, c.is_nullable,
    case
     when u.CONSTRAINT_TYPE = 'PRIMARY KEY' then 'primary key'
     else ''
    end as pk
 FROM INFORMATION_SCHEMA.COLUMNS as c
 LEFT OUTER JOIN information_schema.CONSTRAINT_table_USAGE as u
 ON c.table_name = u.table_name
 Order by table_name

您当然不能在 SELECT 中打印

【讨论】：

Msg 102 - 你错过了以 WHEN 开头的那一行。

【解决方案2】：

试试这个：

 SELECT ..., c.is_nullable,
        CASE WHEN u.CONSTRAINT_TYPE = 'PRIMARY KEY' THEN 'primary key'
        ELSE '' 
        END AS KeyType
FROM INFORMATION_SCHEMA.COLUMNS as c

【讨论】：