德比使用INSERT SELECT SQL

Question

我有以下SQL代碼來創建和德比填充了幾桌：

CREATE TABLE GROUPS (
    GRP_ID INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1) PRIMARY KEY, 
    GRP_NAME VARCHAR(256) NOT NULL, 
    DISPLAY_NAME VARCHAR(256)); 

CREATE TABLE USERS (
    USR_ID INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1) PRIMARY KEY, 
    USR_NAME VARCHAR(256) NOT NULL, 
    PASSWORD VARCHAR(512) NOT NULL, 
    DISPLAY_NAME VARCHAR(256)); 

CREATE TABLE USR_GRP_MEMBERSHIP (
    USR_ID INTEGER NOT NULL REFERENCES USERS ON DELETE CASCADE, 
    GRP_ID INTEGER NOT NULL REFERENCES GROUPS ON DELETE CASCADE, 
    CONSTRAINT USR_ID_GRP_ID UNIQUE (USR_ID, GRP_ID)); 

INSERT INTO GROUPS(GRP_NAME, DISPLAY_NAME) VALUES('Users', 'Users'); 
INSERT INTO GROUPS(GRP_NAME, DISPLAY_NAME) VALUES('AdminUsers', 'Administrators'); 
INSERT INTO USERS(USR_NAME, PASSWORD, DISPLAY_NAME) VALUES('user', 'userpwd', 'User'); 
INSERT INTO USERS(USR_NAME, PASSWORD, DISPLAY_NAME) VALUES('admin', 'adminpawd', 'Administrator'); 

#The following code populates the USR_GRP_MEMBERSHIP table using the IDs of users 
#& groups inserted in the previous set of insert statements 

INSERT INTO USR_GRP_MEMBERSHIP VALUES((SELECT USR_ID FROM USERS WHERE USR_NAME = 'user'), (SELECT GRP_ID FROM GROUPS WHERE GRP_NAME = 'Users')); 
INSERT INTO USR_GRP_MEMBERSHIP VALUES((SELECT USR_ID FROM USERS WHERE USR_NAME = 'admin'), (SELECT GRP_ID FROM GROUPS WHERE GRP_NAME = 'Users')); 
INSERT INTO USR_GRP_MEMBERSHIP VALUES((SELECT USR_ID FROM USERS WHERE USR_NAME = 'admin'), (SELECT GRP_ID FROM GROUPS WHERE GRP_NAME = 'AdminUsers')); 

我的問題是：在過去的3個INSERT語句有SELECT聲明中他們重複。如何將這些SELECT語句的輸出存儲在一個變量中並在這3個語句中使用它們？

Answer 1

完成此操作的一種方法是在準備好的語句中使用佔位符？

這裏是一個很好的起點：https://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html

你的聲明，然後將類似：

INSERT INTO USR_GRP_MEMBERSHIP 
VALUES ((SELECT USR_ID FROM USERS WHERE USR_NAME = ?), 
     (SELECT GRP_ID FROM GROUPS WHERE GRP_NAME = ?)); 

，你會替換「用戶」 /「用戶」，「管理員」 /」佔位符用戶'，'管理員'/'AdminUsers'通過使用SetString（兩次），然後ExecuteUpdate，每對。