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1. SUBSTRING º¯Êý

SUBSTRING º¯ÊýÌáÈ¡×Ö·û´®Ö¸¶¨Î»ÖõÄ×Ó×Ö·û´®¡£ÈôÒª»ñÈ¡µ¥¸ö×Ö·û £¬ÇëÌṩÆðʼλÖúͳ¤¶ÈΪ 1¡£

Óï·¨£ºSUBSTRING(string, start_position, length)

ʾÀý£º»ñÈ¡×Ö·û´® “Hello” ÖеĵÚÒ»¸ö×Ö·û£º

SELECT SUBSTRING('Hello', 1, 1);
-- Êä³ö£ºH

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2. CHAR º¯Êý

CHAR º¯Êý´Ó Unicode ×Ö·û¼¯½¨Éèµ¥¸ö×Ö·û¡£Ëü½ÓÊÜÒ»¸öÕûÊýÖµ×÷Ϊ²ÎÊý £¬¸ÃÕûÊýÖµÌåÏÖ Unicode ×Ö·ûµÄ´úÂëµã¡£

Óï·¨£ºCHAR(character_code)

ʾÀý£º»ñÈ¡ Unicode ×Ö·û “A”£¨´úÂëµãΪ 65£©£º

SELECT CHAR(65);
-- Êä³ö£ºA

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3. CHR º¯Êý

CHR º¯ÊýÓë CHAR º¯ÊýÀàËÆ £¬µ«Ëü½ÓÊÜ ASCII ×Ö·ûÂë×÷Ϊ²ÎÊý¡£

Óï·¨£ºCHR(character_code)

ʾÀý£º»ñÈ¡ ASCII ×Ö·û “A”£¨´úÂëµãΪ 65£©£º

SELECT CHR(65);
-- Êä³ö£ºA

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4. UNICHAR º¯Êý

UNICHAR º¯Êý´Ó Unicode ×Ö·û¼¯Öн¨Éèµ¥¸ö×Ö·û¡£Ëü½ÓÊÜÒ»¸ö×Ö·û´®²ÎÊý £¬¸Ã²ÎÊýÖ¸¶¨ÒªÌåÏÖµÄ×Ö·ûµÄÃû³Æ¡£

Óï·¨£ºUNICHAR(character_name)

ʾÀý£º»ñÈ¡ Unicode ×Ö·û “ÐǺŔ£¨Ãû³ÆΪ “*£©£º

SELECT UNICHAR('*');
-- Êä³ö£º*

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