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-- col1 ×Ö¶ÎÉèÖÃΪ null
INSERT INTO tabtest (id, col1) VALUES(1, NULL);
-- col1 ×Ö¶ÎÉèÖÃΪ ‘’
INSERT INTO tabtest (id, col1) VALUES(2, '');
-- col1 ×Ö¶ÎÉèÖÃΪ ‘a’
INSERT INTO tabtest (id, col1) VALUES(3, 'a');
 
4¡¢ÖØн¨Á¢²éѯÇëÇó£¬Í¨¹ý sql Ìí¼ÓÐÂ×ֶΠcol2
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ALTER TABLE tabTest ADD COLUMN col2 CHAR(1);
 
5¡¢Ê¹ÓÃÈçÏÂsql ÔÙ´ÎÏò tabTest Ìí¼ÓÐÂÊý¾Ý
-- col1£¬col2 ×Ö¶ÎÉèÖÃΪ null
INSERT INTO tabtest(id, col1, col2) VALUES(4, NULL, NULL);
-- col1£¬col2 ×Ö¶ÎÉèÖÃΪ ‘’
INSERT INTO tabtest(id, col1, col2) VALUES(5, '', '');    
-- col1£¬col2 ×Ö¶ÎÉèÖÃΪ ‘a’
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SELECT id, len(col1) AS col1_³¤¶È, len(col2) AS col2_³¤¶È
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ÄÕÈ赀 access jet Óï·¨

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Sql Server ºÍ Access ²Ù×÷Êý¾Ý¿â½á¹¹SqlÓï¾ä

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create table [±íÃû]
(
[×Ô¶¯±àºÅ×Ö¶Î] int IDENTITY (1,1) PRIMARY KEY ,
[×Ö¶Î1] nVarChar(50) default 'ĬÈÏÖµ' null ,
[×Ö¶Î2] ntext null ,
[×Ö¶Î3] datetime,
[×Ö¶Î4] money null ,
[×Ö¶Î5] int default 0,
[×Ö¶Î6] Decimal (12,4) default 0,
[×Ö¶Î7] image null ,
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