别名

Drizzle 支持对表、列、子查询和 CTE 进行别名处理——这与 SQL 的 AS 关键字直接对应。

表别名

你可以使用 alias 函数为表设置别名。当你需要多次连接同一张表时，这很有用，例如在员工及其经理这样的自引用关系中：

import { alias, pgTable, integer, text } from "drizzle-orm/pg-core";

const employees = pgTable("employees", {
  id: integer().primaryKey(),
  name: text(),
  managerId: integer("manager_id"),
});

const manager = alias(employees, "manager");

await db.select({
  employeeName: employees.name,
  managerName: manager.name,
})
  .from(employees)
  .leftJoin(manager, eq(employees.managerId, manager.id));

select "employees"."name", "manager"."name"
from "employees"
left join "employees" as "manager" on "employees"."manager_id" = "manager"."id";

列别名

你可以使用列上的 .as() 方法以及 sql 表达式来为列设置别名。这与 SQL 的 AS 关键字直接对应，并让你能够控制查询结果中列的名称：

const result = await db.select({
  id: users.id,
  lowerName: users.name.as("lower_name"),
}).from(users);

select "id", "name" as "lower_name" from "users";

你也可以在 sql 表达式中使用 .as()：

const result = await db.select({
  id: users.id,
  lowerName: sql<string>`lower(${users.name})`.as("lower_name"),
}).from(users);

select "id", lower("name") as "lower_name" from "users";

子查询别名

当将子查询用作数据源时，你必须使用 .as() 提供别名。这使你能够在外层查询中引用子查询的列：

const sq = db.select().from(users).where(eq(users.id, 42)).as('sq');

const result = await db.select().from(sq);

select "id", "name", "age" from (select "id", "name", "age" from "users" where "users"."id" = 42) "sq";

子查询也可以用于连接中：

const sq = db.select().from(users).where(eq(users.id, 42)).as('sq');

const result = await db.select().from(users).leftJoin(sq, eq(users.id, sq.id));

select "users"."id", "users"."name", "users"."age", "sq"."id", "sq"."name", "sq"."age"
  from "users"
  left join (select "id", "name", "age" from "users" where "users"."id" = 42) "sq"
    on "users"."id" = "sq"."id";

CTE 别名

公共表表达式（CTE）使用 db.$with('alias') 进行别名处理。别名名称用于在主查询中引用该 CTE：

const sq = db.$with('sq').as(db.select().from(users).where(eq(users.id, 42)));

const result = await db.with(sq).select().from(sq);

with "sq" as (select "id", "name", "age" from "users" where "users"."id" = 42)
select "id", "name", "age" from "sq";

当在 CTE 中使用 sql 表达式时，你需要用 .as() 为它们设置别名，才能在外层查询中引用它们：

const sq = db.$with('sq').as(db.select({
  name: sql<string>`upper(${users.name})`.as('name'),
}).from(users));

const result = await db.with(sq).select({ name: sq.name }).from(sq);

with "sq" as (select upper("name") as "name" from "users")
select "name" from "sq";