我用表"user"创建了模式"customer1",我正在尝试使用Connection.setSchema()从JDBC连接它:
String url = "jdbc:postgresql://localhost/project";
Properties props = new Properties();
props.setProperty("user", "postgres");
props.setProperty("password", "postgres");
try (Connection conn = DriverManager.getConnection(url, props)) {
conn.setSchema("customer1");
try (Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery("SHOW search_path")) {
rs.next();
System.out.println("search_path: " + rs.getString(1));
}
try (Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery("SELECT name FROM user LIMIT 1")) {
if (rs.next()) {
System.out.println("user name: " + rs.getString("name"));
}
}
}
此代码打印:
search_path: customer1
然后它抛出带有消息的 PSQLException:
ERROR: column "name" does not exist
如果我在 SELECT 查询中限定"用户"表:
try (Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery("SELECT name FROM customer1.user LIMIT 1")) {
if (rs.next()) {
System.out.println("user name: " + rs.getString("name"));
}
}
然后打印:
search_path: customer1
user name: name1
并且不会发生错误。我正在使用JDBC驱动程序42.2.2和PostgreSQL服务器10.4。为什么设置架构不起作用?
user
是一个内置函数(和一个关键字)。所以你不能真正使用它作为表名:
psql (10.4)
Type "help" for help.
postgres=# select user;
user
----------
postgres
(1 row)
postgres=# select * from user;
user
----------
postgres
(1 row)
而且因为它是一个函数,所以它没有列name
.
postgres=# select name from user;
ERROR: column "name" does not exist
LINE 1: select name from user;
^
postgres=#
如果您限定了表,那么很明显您引用的不是函数,而是表。
您始终可以使用架构限定表名,也可以使用双引号:select name from "user";
或者只是查找不与内置函数冲突的表名。