计数显示 MySQL 中的变量结果

Question

我正在阅读这篇文章，似乎没有办法做这样的事情：

SELECT COUNT(*) 
WHERE SHOW VARIABLES 
WHERE Variable_name = 'innodb_ft_cache_size'

我可以执行以下操作，但这在 MySQL 5.7 中不起作用（表中没有变量）

SELECT COUNT(*) 
FROM information_schema.GLOBAL_VARIABLES 
WHERE Variable_name = 'innodb_ft_cache_size' (always returns 0)

我需要这样做的原因是在存储过程中检测他们是否有能力做全文。它需要在MySQLMySQL 和变体中工作，所以我不能简单地解析@@verison.

有没有另一种方法可以做到这一点？

这是一个works on 5.5,5.6, and 5.7用于检测是否存在全文功能的存储过程。这也应该适用于 mysql 变体

begin
set @supports_ft = 0;
set @information_schema_exists := (SELECT COUNT(SCHEMA_NAME) FROM information_schema.SCHEMATA WHERE SCHEMA_NAME = 'information_schema');

if @information_schema_exists > 0 then
    set @information_schema_exists_global_vars_exists := (SELECT COUNT(*) FROM information_schema.TABLES WHERE TABLE_SCHEMA = 'information_schema' AND TABLE_NAME = 'GLOBAL_VARIABLES');
        if @information_schema_exists_global_vars_exists > 0 then
            set @supports_ft := (SELECT COUNT(*) FROM information_schema.GLOBAL_VARIABLES WHERE VARIABLE_NAME = 'innodb_ft_cache_size');
        end if;
end if;

if @supports_ft = 0 then
    set @performance_schema_exists := (SELECT COUNT(SCHEMA_NAME) FROM information_schema.SCHEMATA WHERE SCHEMA_NAME = 'performance_schema');
    if @performance_schema_exists > 0 then
        set @performance_schema_exists_global_vars_exists := (SELECT COUNT(*) FROM information_schema.TABLES WHERE TABLE_SCHEMA = 'performance_schema' AND TABLE_NAME = 'GLOBAL_VARIABLES');
            if @performance_schema_exists_global_vars_exists > 0 then
                set @supports_ft := (SELECT COUNT(*) FROM performance_schema.GLOBAL_VARIABLES WHERE VARIABLE_NAME = 'innodb_ft_cache_size');
            end if;
    end if;
end if;

Answer 1

你可以运行

flush status;
show global variables like 'innodb_ft_cache_size';
show status like 'handler_read_rnd_next';

如果它是 2（或增加 2），那么您就拥有了该变量。如果它是 1（或增加 1），则不需要。

这应该适用于每个版本。