[SQL] Support MySQL function

[dongzl]

What would you like to be added:

Why is this needed:

math function

• ABS
• CEIL
• FLOOR
• RAND
• SIGN
• PI
• TRUNCATE
• ROUND
• POWER
• SQRT
• EXP
• MOD

cast function

• CAST_UNSIGNED
• [SQL] Support MySQL CAST_SIGNED function. #465
• CAST_CHARSET
• CAST_NCHAR
• CAST_CHAR
• [SQL] Support MySQL CAST_DATE function. #569
• [SQL] Support MySQL CAST_DATETIME function. #568
• [SQL] Support MySQL CAST_TIME function. #570
• [SQL] Support MySQL CAST_DECIMAL function. #571

IF function

• [SQL] Support MySQL IF & IFNULL function. #493

crypto function

• MD5
• [SQL] Support MySQL SHA1 & SHA function. #500
• SHA1

String function

• [SQL] Support MySQL CHAR_LENGTH function. #501
• [SQL] Support MySQL LENGTH function. #502
• [SQL] Support MySQL CONCAT function. #503
• [SQL] Support MySQL CONCAT_WS function. #505
• [SQL] Support MySQL UPPER function. #513
• [SQL] Support MySQL LOWER function. #517
• [SQL] Support MySQl LEFT function. #518
• [SQL] Support MySQL RIGHT function. #519
• [SQL] Support MySQL REPEAT function. #520
• [SQL] Support MySQL SPACE function. #537
• [SQL] Support MySQL REPLACE function. #538
• [SQL] Support MySQL STRCMP function. #539
• [SQL] Support MySQL SUBSTRING function. #542
• [SQL] Support MySQL REVERSE function. #543
• [SQL] Support MySQL LTRIM function. #552
• [SQL] Support MySQL RTRIM function. #553
• [SQL] Support MySQL LPAD function. #563
• [SQL] Support MySQL RPAD function. #564

[dongzl]

ref #454 #434

[dongzl]

ref #460 #465 #477 #483 #484 #493