wehub-resource-sync
58 lines
2.1 KiB
Markdown
58 lines
2.1 KiB
Markdown
# New features
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## `USE INDEX`, `FORCE INDEX` and `IGNORE INDEX` for MySQL
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In MySQL, the statements USE INDEX, FORCE INDEX, and IGNORE INDEX are hints used in SQL queries to influence how the query optimizer selects indexes. These hints provide fine-grained control over index usage, helping optimize performance when the default behavior of the optimizer is not ideal.
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### Use Index
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The `USE INDEX` hint suggests to the optimizer which indexes to consider when processing the query. The optimizer is not forced to use these indexes but will prioritize them if they are suitable.
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```ts
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export const users = mysqlTable('users', {
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id: int('id').primaryKey(),
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name: varchar('name', { length: 100 }).notNull(),
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}, () => [usersTableNameIndex]);
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const usersTableNameIndex = index('users_name_index').on(users.name);
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await db.select()
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.from(users, { useIndex: usersTableNameIndex })
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.where(eq(users.name, 'David'));
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```
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### Ignore Index
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The `IGNORE INDEX` hint tells the optimizer to avoid using specific indexes for the query. MySQL will consider all other indexes (if any) or perform a full table scan if necessary.
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```ts
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export const users = mysqlTable('users', {
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id: int('id').primaryKey(),
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name: varchar('name', { length: 100 }).notNull(),
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}, () => [usersTableNameIndex]);
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const usersTableNameIndex = index('users_name_index').on(users.name);
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await db.select()
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.from(users, { ignoreIndex: usersTableNameIndex })
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.where(eq(users.name, 'David'));
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```
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### Force Index
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The `FORCE INDEX` hint forces the optimizer to use the specified index(es) for the query. If the specified index cannot be used, MySQL will not fall back to other indexes; it might resort to a full table scan instead.
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```ts copy
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export const users = mysqlTable('users', {
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id: int('id').primaryKey(),
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name: varchar('name', { length: 100 }).notNull(),
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}, () => [usersTableNameIndex]);
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const usersTableNameIndex = index('users_name_index').on(users.name);
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await db.select()
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.from(users, { forceIndex: usersTableNameIndex })
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.where(eq(users.name, 'David'));
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```
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You can also combine those hints and use multiple indexes in a query if you need |