Informix 系统表（syscolumns）中字段类型（coltype）字段的含义

0 = CHAR
1 = SMALLINT
2 = INTEGE R
3 = FLOAT
4 = SMALLFLOAT
5 = DECIMAL
6 = SERIAL *
7 = DATE
8 = MONEY
9 = NULL
10 = DATETIME
11 = BYTE
12 = TEXT
13 = VARCHAR
14 = INTERVAL
15 = NCHAR
16 = NVARCHAR
17 = INT8
18 = SERIAL8 *
19 = SET
20 = MULTISET
21 = LIST
22 = Unnamed ROW
40 = Variable-length opaque type (LVARCHAR)
4118 = Named ROW

如果，某字段要求非空，则在原数字上加256，
如：某字段coltype=262,那么,262-256=6，该字段就应该为：SERIAL not NULL 类型！
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