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51 lines
1.3 KiB
51 lines
1.3 KiB
2 years ago
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# Hints
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Optimizer/Index/Comment Hints support for GORM
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## Optimizer Hints
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```go
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import "gorm.io/hints"
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DB.Clauses(hints.New("hint")).Find(&User{})
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// SELECT * /*+ hint */ FROM `users`
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```
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## Index Hints
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```go
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import "gorm.io/hints"
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DB.Clauses(hints.UseIndex("idx_user_name")).Find(&User{})
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// SELECT * FROM `users` USE INDEX (`idx_user_name`)
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DB.Clauses(hints.ForceIndex("idx_user_name", "idx_user_id").ForJoin()).Find(&User{})
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// SELECT * FROM `users` FORCE INDEX FOR JOIN (`idx_user_name`,`idx_user_id`)"
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DB.Clauses(
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hints.ForceIndex("idx_user_name", "idx_user_id").ForOrderBy(),
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hints.IgnoreIndex("idx_user_name").ForGroupBy(),
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).Find(&User{})
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// SELECT * FROM `users` FORCE INDEX FOR ORDER BY (`idx_user_name`,`idx_user_id`) IGNORE INDEX FOR GROUP BY (`idx_user_name`)"
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```
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## Comment Hints
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```go
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import "gorm.io/hints"
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DB.Clauses(hints.Comment("select", "master")).Find(&User{})
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// SELECT /*master*/ * FROM `users`;
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DB.Clauses(hints.CommentBefore("insert", "node2")).Create(&user)
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// /*node2*/ INSERT INTO `users` ...;
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DB.Clauses(hints.CommentAfter("select", "node2")).Create(&user)
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// /*node2*/ INSERT INTO `users` ...;
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DB.Clauses(hints.CommentAfter("where", "hint")).Find(&User{}, "id = ?", 1)
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// SELECT * FROM `users` WHERE id = ? /* hint */
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```
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