一些Informix+SQL函数的用法及日期操作

一些Informix SQL函数的用法一、内部函数1、内部合计函数1）COUNT（*）返回行数2）COUNT（DISTINCT COLNAME）返回指定列中唯一值的个数3）SUM（COLNAME/EXPRESSION）返回指定列或表达式的数值和；4）SUM（DISTINCT COLNAME）返回指定列中唯一值的和5）A VG（COLNAME/EXPRESSION）返回指定列或表达式中的数值平均值6）A VG（DISTINCT COLNAME）返回指定列中唯一值的平均值7）MIN（COLNAME/EXPRESSION）返回指定列或表达式中的数值最小值8）MAX（COLNAME/EXPRESSION）返回指定列或表达式中的数值最大值2、日期与时间函数1）DAY（DATE/DATETIME EXPRESSION）返回指定表达式中的当月几号2）MONTH（DATE/DATETIME EXPRESSION）返回指定表达式中的月份3）YEAR（DA TE/DATETIME EXPRESSION）返回指定表达式中的年份4）WEEKDAY（DA TE/DA TETIME EXPRESSION）返回指定表达式中的当周星期几5）DATE（NOT DATE EXPRESSION）返回指定表达式代表的日期值6）TODAY返回当前日期的日期值7）CURRENT[first to last]返回当前日期的日期时间值8）COLNAME/EXPRESSION UNITS PRECISION返回指定精度的指定单位数9）MDY（MONTH，DAY，YEAR）返回标识指定年、月、日的日期值10）DATETIME（DA TE/DA TETIME EXPRESSION）FIRST TO LAST 返回表达式代表的日期时间值11）INTERV AL（DA TE/DA TETIME EXPRESSION）FIRST TO LAST 返回表达式代表的时间间隔值12）EXTEND（DATE/DATETIME EXPRESSION，[first to last]）返回经过调整的日期或日期时间值例子1、和UNITS合用，指定日期或时间单位(year,month,day,hour,minute,second,fraction)：let tmp_date = TODAY+ 3 UNITS day例子2、let tmp_date = MDY(10,30,2002)-- 2002-10-30例子3、let tmp_date = today + interval(7) day to day--当前时间加上7天；注：该功能与1相似；例子4、EXTEND转换日期或日期时间值let tmp_inthour = EXTEND(datetime1,hour to hour)3、代数函数1）ABS(COLNAME/EXPRESSION)：取绝对值2）MOD（COLNAME/EXPRESSION，DIVISOR）返回除以除数后的模（余数）3）POW（COLNAME/EXPRESSION，EXPONENT）返回一个值的指数冥例子：let tmp_float = pow(2,3)--8.000000004）ROOT（COLNAME/EXPRESSION，[index]）返回指定列或表达式的根值5）SQRT（COLNAME/EXPRESSION）返回指定列或表达式的平方根值6）ROUND（COLNAME/EXPRESSION，[factor]）返回指定列或表达式的圆整化值7）TRUNC（COLNAME/EXPRESSION，[factor]）返回指定列或表达式的截尾值说明：上两者中FACTOR指定小数位数，若不指定，则为0；若为负数，则整化到小数点左边；注：ROUND是在指定位上进行4舍5入；TRUNC是在指定位上直接截断；let tmp_float = ROUND(4.555,2) --4.56let tmp_float = TRUNC(4.555,2) --4.554、指数与对数函数1）EXP（COLNAME/EXPRESSION）返回指定列或表达式的指数值2）LOGN（COLNAME/EXPRESSION）返回指定列或表达式的自然对数值3）LOG10（COLNAME/EXPRESSION）返回指定列或表达式的底数位10的对数值5、三角函数1）COS（RADIAN EXPRESSION）返回指定弧度表达式的余弦值2）SIN（RADIAN EXPRESSION）正弦3）TAN（RADIAN EXPRESSION）正切4）ACOS（RADIAN EXPRESSION）反余弦5）ASIN（RADIAN EXPRESSION）反正弦6）ATAN（RADIAN EXPRESSION）反正切7）ATAN2（X，Y）返回坐标（X，Y）的极坐标角度组件6、统计函数1）RANGE（COLNAME）返回指定列的最大值与最小值之差= MAX （COLNAME）-MIN（COLNAME）2）V ARIANCE（COLNAME）返回指定列的样本方差；3）STDEV（COLNAME）返回指定列的标准偏差；7、其他函数1）USER返回当前用户名2）HEX（COLNAME/EXPRESSION）返回指定列或表达式的十六进制值3）LENGTH（COLNAME/EXPRESSION）返回指定字符列或表达式的长度4）TRIM（COLNAME/EXPRESSION）删除指定列或表达式前后的字符5）COLNAME/EXPRESSION || COLNAME/EXPRESSION返回并在一起的字符；二、IDS内部函数1、DBSERVERNAME返回数据库服务器名let tmp_char=DBSERVERNAME2、SITENAME返回数据库服务器名let tmp_char=SITENAME说明：两者功能相同；3、DBINFO（‘SPECIAL_KEYWORD')返回只关键字值例子1：返回数据中每个表的DBSPACE名称select dbinfo('dbspace',partnum),tabname from systableswhere tabid>99 and tabtype='T'(OK)例子2：返回任何表中插入的最后一个SERIAL值select dbinfo('sqlca.sqlerrd1') from systables where tabid = 1例子3：返回最后一个SELECT，INSERT，UPDATE，DELETE或EXECUTE PROCEDURE语句处理的行数；select dbinfo('sqlca.sqlerrd2') from systables where tabid=1;Date Manipulation (日期操作)One of the more difficult concepts in Informix's handling of date and time values concerns the use of the variables in arithmetic or relational expressions. You can add or subtract DA TE and DA TETIME variables from each other. You can add or subtract an INTERV AL to a DATE or DA TETIME. Table 1 shows the results of different types of operations on DA TE and DA TETIME values.Notice that it's always okay to subtract one DA TE or DATETIME value from another, as shown here:CURRENT - "07/01/1950" = INTERV AL (my age)"12/25/2000" – CURRENT = INTERV AL (how long till Xmas?)In such a case, the result is always an INTERV AL variable. It would make no sense to add two DA TE or DATETIME values together. What could such an addition represent?UNITS KeywordWhen working with INTERV AL values, sometimes it is necessary to specify the precision with which you are dealing. For example, suppose you have the following field defined:lead_time INTERV AL DAY to DAYTo add 10 days to the lead time you could use a SQL statement like this:SELECT lead_time + INTERV AL(10) DAY to DAYFROM orders;You could achieve the same results using the UNITS keyword:SELECT lead_time + 10 UNITS DAYFROM orders;Like most other programming languages, SQL often allows you to achieve the same ends with different statements. Sometimes the choice is one of personal style. Other times, one format fits in better with a structured style of code writing than another format does.FunctionsThere are several built-in functions that affect date and time calculations. They can apply to either DA TE or DATETIME values, with some exceptions.TODAYThe TODAY function returns a DA TE data value representing the current date. For example, you could execute a SQL function like this:UPDATE member SET change_date = TODAYWHER member_number = 12345;CURRENTThe CURRENT function is similar to the TODAY function, except it returns a DATETIME value. Without specific qualifiers, the default is YEAR to FRACTION(3). You can change the precision by using the same YEAR to FRACTION qualifiers as you use for DATETIMES. Thus, this would be legal:SELECT * from memberWHERE elapsed_time < CURRENT YEAR to DAYDATEThe DATE function takes as input a non-DA TE value such as CHAR, DATETIME, or INTEGER and returns the corresponding DATE value. For example, the following SQL translates a CHARACTER value to a DATE:SELECT * from memberWHERE enrollment_date > DA TE('01/01/99');DAYThis function returns an integer representing the day of the month. Here's an example:SELECT * from memberWHERE DAY(enrollment_date) > DAY(CURRENT);MONTHThis performs like the DAY function except it returns an integer between 1 and 12 representing the month:SELECT * from memberWHERE enrollment_date > MONTH('01/01/99');WEEKDAYThis returns an integer representing the day of the week, with 0 being Sunday and 6 being Saturday:SELECT * from memberWHERE WEEKDAY(enrollment_date) > WEEKDAY(CURRENT);YEARThis function is like the ones above, only it returns a four-digit integer representing the year.EXTENDThis function allows you to use different precisions in a DATETIME than you have specified in the declaration of the variable. It uses the same FIRST to LAST syntax as the DATETIME variables. This function is used to adjust the precision of a DA TETIME variable to match the precision of an INTERV AL that you are using in a calculation. If the INTERV AL value has fields that are not part of the DATETIME value that you are using in a calculation, use the EXTEND function to adjust the precision of the DA TETIME. EXTEND can either increase or decrease the precision of a DATETIME, depending upon the FIRST and LAST values.Suppose myvariable is declared as DA TETIME YEAR to DAY. If you want to add or subtract an INTERV AL defined as MINUTE, you first have to extend the DATETIME as follows:SELECT EXTEND(myvariable, YEAR to MINUTE) –INTERV AL(5) MINUTE to MINUTEFROM memberThe resulting value will be DATETIME YEAR to MINUTE;MDYThe MDY function converts three-integer values into a DATE format. The first integer is the month and must evaluate to an integer in the range 1–12. The second integer is the day and must evaluate to a number in the range from 1 to however many days are in the particular month (28–31). The third expression is the year and must be a four-digit integer. Thus, the following MDY functions would each be valid:MDY(7,1,1950)returns a DATE of "07/01/50"MDY(MONTH(TODAY), 1, YEAR(TODAY))returns a DATE equal to the first day of the current month in the current yearInformix has extensive capabilities for manipulating dates and times, which can make for long and complex SQL statements. Using the three time-related data types and the time-related functions and keywords, you can accomplish almost any type of manipulation of time data. Unfortunately, getting there may be cryptic and painful. If you regularly do extensive date and time manipulation, you should understand all of the intricacies of these data structures.Have fun!。