Question

所以，这是条件。

我有User_tbl，其代码如下

CREATE TABLE Users_tbl (
    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    username TEXT,
    password TEXT,
    user_type INT
);

user_type是0,1或2.如果是0那么它是玩家，1是教练，2是观众。

现在，我想创建一个新表，其中包含coach列表。架构将是

CREATE TABLE coach_tbl(
coach_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT
)

我需要的是，当Users_tbl中的条目有user_type = 1时，它应该触发另一个查询，该查询将在coach_tbl中创建一个条目并填写列。它应该动态发生。

Answer 1

以下TRIGGER将实现您的目标： -

CREATE TRIGGER setup_coach 
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
    BEGIN 
        INSERT INTO coach_tbl (username, password) VALUES(new.username,new.password);
    END
;

以下用于测试上述内容： -

DROP TABLE IF EXISTS Users_tbl;
CREATE TABLE IF NOT EXISTS Users_tbl (
    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    username TEXT,
    password TEXT,
    user_type INT
);
DROP TABLE IF EXISTS coach_tbl;
CREATE TABLE IF NOT EXISTS coach_tbl(
coach_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT
);

CREATE TRIGGER setup_coach 
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
    BEGIN 
        INSERT INTO coach_tbl (username, password) VALUES(new.username,new.password);
    END
;
INSERT INTO Users_tbl (username, password,user_type) 
VALUES 
    ('Fred','fred1234',0),
    ('Bert','bert1234',1),
    ('Harold','harold1234',0),
    ('Alan','alan1234',1);

结果是： -

补充（又名为什么不是上述）

存储完全相同的值。即复制它们，与规范化相反，可能导致问题。例如如果（使用上述）“Bert”的名字或“密码”改变了，你必须在两个地方改变它。目前没有必要复制这些数据，因为它很容易获得

例如，如果您想列出可以使用的教练： -

SELECT username FROM coach_tbl;

但是，使用以下内容完全相同但没有附加表： -

SELECT username FROM Users_tbl WHERE user_type = 1;

假设您有教练特定信息，例如说教练的次数，那么您可以有一个额外的表格，如： -

CREATE TABLE IF NOT EXISTS coaching_information
    (
    user_id_reference INTEGER REFERENCES Users_tbl(id),
    number_of_times_coaching INTEGER DEFAULT 0
    )
;

与TRIGGER一起自动添加默认辅导信息： -

CREATE TRIGGER autoadd_coaching_information_entry
AFTER INSERT ON Users_tbl 
WHEN new.user_type = 1
BEGIN 
    INSERT INTO coaching_information
        (user_id_reference)
        VALUES (new.id)
        ;
END
;

注意！无需设置 number_of_times_coaching 列，因为它默认为0。

假设所有TABLES都已清空，然后使用（再次）： -

INSERT INTO Users_tbl (username, password,user_type) 
VALUES 
    ('Fred','fred1234',0),
    ('Bert','bert1234',1),
    ('Harold','harold1234',0),
    ('Alan','alan1234',1);

导致： -

2指伯特，4指艾伦

然后你可以列出所有没有执教过的教练（选择因为没有更新教练信息的懒惰）： -

SELECT 'Coach '||username||' is up for a coaching experience.' AS coaching_needed 
FROM coaching_information 
JOIN Users_tbl ON Users_tbl.id = coaching_information.user_id_reference
WHERE coaching_information.number_of_times_coaching < 1

结果将是： -

Say Bert改名为Charles，例如使用UPDATE Users_tbl SET username = 'Charles' WHERE username = 'Bert';

然后只需更改1，上述查询的结果就是： -

用于测试上述内容的完整SQL是： -

DROP TABLE IF EXISTS coach_tbl;
DROP TABLE IF EXISTS Users_tbl;
CREATE TABLE IF NOT EXISTS Users_tbl (
    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    username TEXT,
    password TEXT,
    user_type INT
);

DROP TRIGGER IF EXISTS setup_coach; -- get rid of defunct TRIGGER
CREATE TABLE IF NOT EXISTS coaching_information
    (
    user_id_reference INTEGER REFERENCES Users_tbl(id) ON DELETE CASCADE,
        -- Note ON DELETE CASCADE will automatically delete a coach should 
        -- the coach's User_tbl entry be deleted i.e. the deletion is propoagted
        -- to the children of the parent.
        -- (could also use ON UPDATE CASCADE but unlikely to change the underlying id)
    number_of_times_coaching INTEGER DEFAULT 0
    )
;

DROP TRIGGER IF EXISTS autoadd_coaching_information_entry;
CREATE TRIGGER autoadd_coaching_information_entry
AFTER INSERT ON Users_tbl 
WHEN new.user_type = 1
BEGIN 
    INSERT INTO coaching_information
        (user_id_reference)
        VALUES (new.id)
        ;
END

;
INSERT INTO Users_tbl (username, password,user_type) 
VALUES 
    ('Fred','fred1234',0),
    ('Bert','bert1234',1),
    ('Harold','harold1234',0),
    ('Alan','alan1234',1)
;
--
-- Note! oncommmenting this will change Bert's name to Charles
--UPDATE Users_tbl SET username = 'Charles' WHERE username = 'Bert';
--
SELECT 'Coach '||username||' is up for a coaching experience.' AS coaching_needed 
FROM coaching_information 
JOIN Users_tbl ON Users_tbl.id = coaching_information.user_id_reference
WHERE coaching_information.number_of_times_coaching < 1

如何在条件为真时自动在一个表中添加值

1 个答案:

补充（又名为什么不是上述）