Обсуждение: Converting an expression of one data type to another

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On 10/30/2014 07:44 PM, rohtodeveloper wrote:
> Dear
> 
> I'm doing a job about converting an expression of one data type to another.
> In SQLServer, there'are two functions to do this job.
> 
> 1. CAST ( expression AS data_type [ ( length ) ] )
> 2. CONVERT ( data_type [ ( length ) ] , expression )
> 
> However, In PostgreSQL, there's only the CAST ( expression AS data_type
> [ ( length ) ] ) function. I have tried the following two ways to
> implenting the CONVERT ( data_type [ ( length ) ] , expression )
> function, but both are failed.
> 
> 1. CREATE FUNCTION ..... 
> The function's arguments can only be expressions but not data_type . 
> 2. Modifying the gram.y .....
> The CONVERT ( data_type [ ( length ) ] , expression ) is in grammer
> conflict with the PostgreSQL self's
> convert(data,src_encoding_name,dest_encoding_name) function. And the
> PostgreSQL self's convert(data,src_encoding_name,dest_encoding_name)
> function cannot be used.
> 
> I wonder whether there's a better way to solve this problem. 
> Any help will be appreciated.
> 
> Best Regards
> Rohtodeveloper


-- Craig Ringer                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services