exec

select子句总是生成一张表，即使只选择一列亦是如此。若需要生成一个标量或者一个向量，可使用exec子句。

当与pivot by 共同使用时，exec语句生成一个矩阵，详情参考 pivot by。

例子

$ sym = `C`MS`MS`MS`IBM`IBM`C`C`C$SYMBOL
$ price= 49.6 29.46 29.52 30.02 174.97 175.23 50.76 50.32 51.29
$ qty = 2200 1900 2100 3200 6800 5400 1300 2500 8800
$ timestamp = [09:34:07,09:36:42,09:36:51,09:36:59,09:32:47,09:35:26,09:34:16,09:34:26,09:38:12]
$ t1 = table(timestamp, sym, qty, price);
$ t1;

timestamp	sym	qty	price
09:34:07	C	2200	49.6
09:36:42	MS	1900	29.46
09:36:51	MS	2100	29.52
09:36:59	MS	3200	30.02
09:32:47	IBM	6800	174.97
09:35:26	IBM	5400	175.23
09:34:16	C	1300	50.76
09:34:26	C	2500	50.32
09:38:12	C	8800	51.29

$ x = select count(price) from t1;
$ x;

count_price
9

$ typestr x;
TABLE

$ y = exec count(price) from t1;
$ y;
9

$ typestr y;
INT

$ x = select price from t1;
$ x;

price
49.6
29.46
29.52
30.02
174.97
175.23
50.76
50.32
51.29

$ typestr x;
TABLE

$ y = exec price from t1;
$ y;
[49.6,29.46,29.52,30.02,174.97,175.23,50.76,50.32,51.29]

$ typestr y;
FAST DOUBLE VECTOR

如果exec语句选择了多列，那么结果和select语句一致，为table类型。

$ y = exec price, qty from t1;
$ y;

price	qty
49.6	2200
29.46	1900
29.52	2100
30.02	3200
174.97	6800
175.23	5400
50.76	1300
50.32	2500
51.29	8800

$ typestr y;
TABLE