SQL -根据计数插入行

-- 创建示例表
CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(100)
);

-- 插入初始数据
INSERT INTO users (id, name) VALUES (1, 'Alice');
INSERT INTO users (id, name) VALUES (2, 'Bob');

-- 查询当前用户数量
SELECT COUNT(*) AS user_count FROM users;

-- 根据计数插入新行
DECLARE @user_count INT;
SET @user_count = (SELECT COUNT(*) FROM users);

IF @user_count < 5
BEGIN
    INSERT INTO users (id, name) VALUES (3, 'Charlie');
END;

BEGIN TRANSACTION;

DECLARE @user_count INT;
SET @user_count = (SELECT COUNT(*) FROM users WITH (UPDLOCK));

IF @user_count < 5
BEGIN
    INSERT INTO users (id, name) VALUES (3, 'Charlie');
END;

COMMIT TRANSACTION;

BEGIN TRY
    INSERT INTO users (id, name) VALUES (3, 'Charlie');
END TRY
BEGIN CATCH
    PRINT 'Insert failed: ' + ERROR_MESSAGE();
END CATCH;