(单选题)6: 执行下面两条SQL语句后:
CREATE TABLE t1
( c1 char(10) NOT NULL PRIMARY KEY,
c2 int,
c3 char(10),
c4 char(10) NOT NULL,
CONSTRAINT c4 UNIQUE (c1,c4) ) //自动创建索引
CREATE INDEX Index1 ON t1 (c2 ASC)
表t1上有几个索引?
A: 0
B: 1
C: 2
D: 3
E: 4
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