GoFrame 數(shù)據(jù)查詢-子查詢特性

?ORM?組件目前支持常見的三種語法的子查詢：?Where?子查詢、?Having?子查詢及?From?子查詢。

Where子查詢

我們可以在?Where?條件中使用子查詢語句，示例：

// 獲取默認(rèn)配置的數(shù)據(jù)庫對象(配置名稱為"default")
db := g.DB()

db.Model("orders").Where("amount > ?", db.Model("orders").Fields("AVG(amount)")).Scan(&orders)
// SELECT * FROM "orders" WHERE amount > (SELECT AVG(amount) FROM "orders")

Having子查詢

我們可以在?Having?條件中使用子查詢語句，示例：

subQuery := db.Model("users").Fields("AVG(age)").WhereLike("name", "name%")
db.Model("users").Fields("AVG(age) as avgage").Group("name").Having("AVG(age) > ?", subQuery).Scan(&results)
// SELECT AVG(age) as avgage FROM `users` GROUP BY `name` HAVING AVG(age) > (SELECT AVG(age) FROM `users` WHERE name LIKE "name%")

From子查詢

我們可以在使用?Model?方法創(chuàng)建模型時使用子查詢語句，示例：

db.Model("? as u", db.Model("users").Fields("name", "age")).Where("age", 18).Scan(&users)
// SELECT * FROM (SELECT `name`,`age` FROM `users`) as u WHERE `age` = 18

subQuery1 := db.Model("users").Fields("name")
subQuery2 := db.Model("pets").Fields("name")
db.Model("? as u, ? as p", subQuery1, subQuery2).Scan(&users)
// SELECT * FROM (SELECT `name` FROM `users`) as u, (SELECT `name` FROM `pets`) as p