MySQL 教程
/ EXISTS
EXISTS
MySQL EXISTS 運算符
EXISTS 運算符用于測試子查詢中是否存在任何記錄。
如果子查詢返回一條或多條記錄，EXISTS 運算符返回 TRUE。
EXISTS 語法
SELECT column_name(s)
FROM table_name
WHERE
EXISTS(SELECT column_name FROM table_name WHERE
condition);演示數(shù)據(jù)庫
以下是 Northwind 示例數(shù)據(jù)庫中 "Products" 產(chǎn)品表的選擇:
| ProductID | ProductName | SupplierID | CategoryID | Unit | Price |
|---|---|---|---|---|---|
| 1 | Chais | 1 | 1 | 10 boxes x 20 bags | 18 |
| 2 | Chang | 1 | 1 | 24 - 12 oz bottles | 19 |
| 3 | Aniseed Syrup | 1 | 2 | 12 - 550 ml bottles | 10 |
| 4 | Chef Anton's Cajun Seasoning | 2 | 2 | 48 - 6 oz jars | 22 |
| 5 | Chef Anton's Gumbo Mix | 2 | 2 | 36 boxes | 21.35 |
從“供應(yīng)商”表中選擇:
| SupplierID | SupplierName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
| 1 | Exotic Liquid | Charlotte Cooper | 49 Gilbert St. | London | EC1 4SD | UK |
| 2 | New Orleans Cajun Delights | Shelley Burke | P.O. Box 78934 | New Orleans | 70117 | USA |
| 3 | Grandma Kelly's Homestead | Regina Murphy | 707 Oxford Rd. | Ann Arbor | 48104 | USA |
| 4 | Tokyo Traders | Yoshi Nagase | 9-8 Sekimai Musashino-shi | Tokyo | 100 | Japan |
MySQL EXISTS 示例
以下 SQL 語句返回 TRUE 并列出產(chǎn)品價格低于 20 的供應(yīng)商:
實例
SELECT SupplierNameFROM SuppliersWHERE EXISTS (SELECT ProductName FROM
Products WHERE Products.SupplierID = Suppliers.supplierID AND Price < 20);
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以下 SQL 語句返回 TRUE 并列出產(chǎn)品價格等于 22 的供應(yīng)商:
實例
SELECT SupplierNameFROM SuppliersWHERE EXISTS (SELECT ProductName FROM
Products WHERE Products.SupplierID = Suppliers.supplierID AND Price = 22);
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