用于什么目的?

• IF 最快的是 IF EXISTS (SELECT * FROM Table)...
• 对于结果集，SELECT TOP 1 1 FROM Table 返回零行或一行
• 对于恰好有计数(0 或非零)的一行，SELECT COUNT(*) FROM Table

• Quickest for an IF would be IF EXISTS (SELECT * FROM Table)...
• For a result set, SELECT TOP 1 1 FROM Table returns either zero or one rows
• For exactly one row with a count (0 or non-zero), SELECT COUNT(*) FROM Table