SQL - 如何进行有条件的插入操作

Question

使用仅MySQL，我正在查看是否有可能仅在表是新的情况下运行插入语句。我成功地创建了一个用户变量来查看表是否存在。问题在于，您无法在插入语句中使用“WHERE”。有没有想法让这个工作？

// See if the "country" table exists -- saving the result to a variable
SELECT
    @table_exists := COUNT(*)
FROM
    information_schema.TABLES
WHERE
    TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'country';

// Create the table if it doesn't exist
CREATE TABLE IF NOT EXISTS country (
    id INT unsigned auto_increment primary key,
    name VARCHAR(64)
);

// Insert data into the table if @table_exists > 0
INSERT INTO country (name) VALUES ('Afghanistan'),('Aland Islands') WHERE 0 < @table_exists;

- Matt

Answer 1

IF @TableExists > 0 THEN
   BEGIN
       INSERT INTO country (name) VALUES ('Afghanistan'),('Aland Islands');
   END

- Jonathan Holland

Answer 2

使用if语句代替where子句：

http://dev.mysql.com/doc/refman/5.0/en/if-statement.html

- mmattax