SAPHANA学习（12）：SQL Function(L)

81.LAG

LAG( <expression> [, <offset> [, <default_expr> ] ] ) <window_specification>

<offset>非负整数，默认1；

<default_expr>,如果超过记录，返回<default_expr>值；如果没设置，返回null;

返回当前行之前偏移行的值。

LEAD( <expression> [, <offset> [, <default_expr> ] ] ) <window_specification>

返回当前行之后的行偏移量。

SELECT TS_ID,VALUE1,VALUE2,
       LEAD(VALUE1) OVER (PARTITION BY TS_ID ORDER BY VALUE1) AS lead, 
       LEAD(VALUE1,VALUE2,-VALUE1) OVER (PARTITION BY TS_ID ORDER BY VALUE1) AS lead2, 
       LAG(VALUE1) OVER (PARTITION BY TS_ID ORDER BY VALUE1) AS lag, 
       LAG(VALUE1,VALUE2,-VALUE1) OVER (PARTITION BY TS_ID ORDER BY VALUE1) AS lag2
       FROM CORRELATIONTABLE3;

82.LANGUAGE(<column_name>)

CREATE COLUMN TABLE TEST_LANGUAGE (CONTENT TEXT FAST PREPROCESS OFF LANGUAGE DETECTION('EN','DE'));
INSERT INTO TEST_LANGUAGE VALUES('This is a very short example.');
INSERT INTO TEST_LANGUAGE VALUES('Dies ist ein ganz kurzes Beispiel.');
SELECT LANGUAGE(CONTENT),CONTENT FROM TEST_LANGUAGE;

83.LAST_DAY(<date>)

返回包含指定日期月份最后一天

SELECT LAST_DAY(TO_DATE('2010-01-04', 'YYYY-MM-DD')) FROM DUMMY;

84.LAST_VALUE

Aggregate function:

LAST_VALUE( <expression> <order_by_clause> )

Window function:

LAST_VALUE( <expression> <order_by_clause> ) <window_specification>

<order_by_clause> ::= ORDER BY <order_by_expression> [, <order_by_expression> [,...] ]

<order_by_expression> ::= <column_name> [ <collate_clause> ] [ ASC | DESC ] [ NULLS FIRST | NULLS LAST ]

| <column_position> [ <collate_clause> ] [ ASC | DESC ] [ NULLS FIRST | NULLS LAST ]

<collate_clause> ::= COLLATE <collation_name>

SELECT LAST_VALUE ("VALUE" ORDER BY TS_ID) FROM CORRELATIONTABLE;

85.LCASE(<string>)

将<string>转换小写，和LOWER Function功能相似

SELECT LCASE ('TesT') FROM DUMMY;

86.LEAST(<argument_1> [, <argument_2>]...)

返回较小值

SELECT LEAST('aa', 'ab', 'ba', 'bb') FROM DUMMY;

87.LEFT

LEFT(<string>, <number>)

<string>操作字符串

<number>返回字符串长度

返回前<number>个字符串,如果<number>小于1,返回空;

LENGTH(<string>)

返回<string>字符串长度

SELECT LEFT ('Hello', 3) FROM DUMMY;
SELECT LEFT ('Hello', 10) FROM DUMMY;
SELECT LENGTH ('length in char') FROM DUMMY;

88.LINEAR_APPROX

LINEAR_APPROX(<expression> [, <ModeArgument> [, <Value1Argument> [,

<Value2Argument>]]]) OVER ({ SERIES TABLE <table_schema> [<window_partition_by_clause>]

[<window_order_by_clause>] | SERIES(...) [<window_partition_by_clause>]

[<window_order_by_clause>] | [<window_partition_by_clause>] <window_order_by_clause>})

在一个序列中插入值，替换null值

<ModeArgument> ::= EXTRAPOLATION_NONE

| EXTRAPOLATION_LINEAR

| EXTRAPOLATION_CONSTANT

EXTRAPOLATION_NONE：默认模式，此模式不会处理前置或后置null值，只处理中间null值，不需要指定<Value1Argument><Value2Argument>

EXTRAPOLATION_LINEAR：线性外推，<Value1Argument>最小值，<Value2Argument>最大值，

当前置，后置null值推导过程中值不在<Value1Argumen><Value2Argument>范围，替换成<Value1Argument><Value2Argument>

EXTRAPOLATION_CONSTANT：线性外推，前置null值替换为<Value1Argument>，后置null值替换为<Value2Argument>

NON-EQUIDISTANT ：An error occurs if the series is non-equidistant.

MISSING ELEMENTS ALLOWED ：When specified, there must be exactly one ORDER BY column that is compatible with the type of the series period column and the INCREMENT BY value.

PARTITION BY ：If not specified, the SERIES KEY property of the SERIES syntax is used to construct the default PARTITION BY.

ORDER BY ：If not specified, the first PERIOD column is added as an ORDER BY.

CREATE COLUMN TABLE "SparseApproxTable" (ts_id VARCHAR(20), date DAYDATE, val DOUBLE);
INSERT INTO "SparseApproxTable" VALUES('A','2013-11-01', null);
INSERT INTO "SparseApproxTable" VALUES('A','2014-01-01', null);
INSERT INTO "SparseApproxTable" VALUES('A','2014-02-05', 2);
INSERT INTO "SparseApproxTable" VALUES('A','2014-03-07', null);
INSERT INTO "SparseApproxTable" VALUES('A','2014-05-01', 5);
INSERT INTO "SparseApproxTable" VALUES('A','2014-07-27', 7);
INSERT INTO "SparseApproxTable" VALUES('A','2014-12-07', null);
INSERT INTO "SparseApproxTable" VALUES('A','2015-02-07', null);
SELECT LINEAR_APPROX(val, 'EXTRAPOLATION_LINEAR') OVER (
       SERIES (
       SERIES KEY(ts_id) EQUIDISTANT INCREMENT BY INTERVAL 1 MONTH
       MISSING ELEMENTS ALLOWED PERIOD FOR SERIES(date)
       )  
       PARTITION BY ts_id) AS approximated_value
  FROM "SparseApproxTable";

CREATE COLUMN TABLE "InterpolationTable" (TS_ID VARCHAR(20), date DAYDATE, val DOUBLE);
INSERT INTO "InterpolationTable" VALUES('A','2013-09-30', 1);
INSERT INTO "InterpolationTable" VALUES('A','2013-10-01', 2);
INSERT INTO "InterpolationTable" VALUES('A','2013-10-02', null);
INSERT INTO "InterpolationTable" VALUES('A','2013-10-03', 10);
SELECT LINEAR_APPROX (val, 'EXTRAPOLATION_LINEAR') OVER (PARTITION BY TS_ID ORDER BY date) AS LINEAR_APPROX
  FROM "InterpolationTable";

89.LN

LN(<number>)

返回e为底自然对数

LOG(<base>, <number>)

返回<base>为底，值为<number>的自然对数值

<base>大于1的正数，<number>任意正数

SELECT LN(1) FROM DUMMY;
SELECT LOG (2, 8) FROM DUMMY;

90.LOCALTOUTC

LOCALTOUTC (<time> [, <timezone> [, <timezone_dataset>]])

将本地时间转换为UTC时间

<timezone_dataset> ::= { sap | platform }

SELECT LOCALTOUTC (TO_TIMESTAMP('2012-01-01 01:00:00', 'YYYY-MM-DD HH24:MI:SS'), 'EST') FROM DUMMY;
SELECT LOCALTOUTC (TO_TIMESTAMP('2012-01-01 01:00:00', 'YYYY-MM-DD HH24:MI:SS'), 'EST', 'sap') FROM DUMMY;

91.LOCATE

LOCATE( <haystack>, <needle>, [<start_position>] , [ <occurrences> ] )

返回<needle>子字符串在<haystack>中位置,<start_position>匹配开始位置，<occurences>返回第几次匹配结果；

如果没有找到，<occurrences>小于1，返回0；

如果<needle>,<haystack><occurences>为null,返回null;

<start_position>为正数，从左到右匹配；

<start_position>为负数，从右到左匹配;

LOCATE_REGEXPR( [ <regex_position_start_or_after> ] <pattern>

[ FLAG <flag> ]

IN <regex_subject_string>

[ FROM <start_position> ]

[ OCCURRENCE <regex_occurrence> ]

[ GROUP <regex_capture_group> ]

--返回从右到左第一个A
SELECT LOCATE('AACAB', 'A', -1) FROM "DUMMY";
SELECT LOCATE ('length in char','',2) FROM DUMMY;
SELECT LOCATE ('length in char', 'zin') "locate" FROM DUMMY;

92.LOWER(<string>)

将字符串转换小写

SELECT LOWER ('AnT') FROM DUMMY;

93.LPAD

LPAD(<string>, <number> [, <pattern>])

在<string>字符串左边填充<pattern>达到<number>长度

LTRIM(<string> [, <remove_set>])

去前导0

SELECT LPAD ('end', 15, '12345') FROM DUMMY;
--当<number>小于<string>长度，截取左边<number>长度字符串
SELECT LPAD ('end', 2, '12345') FROM DUMMY;
SELECT LTRIM('   end') FROM DUMMY;
--设置<remove_set>，去掉所有前置字符，a,b
SELECT LTRIM ('babababAabend','ab') FROM DUMMY;