Advanced functions in PL SQL

Titles
Analytic Functions
LISTAGG Function
TRANSLATE Function
REGEXP_LIKE Condition
REGEXP_COUNT Function
COALESCE Function
EXTRACT Function
ADD_MONTHS Function
INITCAP Function
INSTR Function
GREATEST Function
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Analytic Functions
• It is true that whatever an analytic function does can be done by native SQL, with join
and sub-queries. But the same routine done by analytic function is always faster, or at
least as fast.
• Syntax
analytic_function([ arguments ]) OVER (analytic_clause)
analytic_clause:
[ query_partition_clause ] [ order_by_clause [ windowing_clause ] ]
• An aggregate function aggregates data from several rows into a single result row.
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How are analytic functions different from group or aggregate functions?
Query-1 returns departments and their employee
count. Most importantly it groups the records into
departments in accordance with the GROUP BY
clause. As such any non-"group by" column is not
allowed in the select clause.
Query-2 Though analytic functions give
aggregate result they do not group the result set.
They return the group value multiple times with
each record. As such any other non-"group by"
column or expression can be present in the select
clause.
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How are analytic functions different from group or aggregate functions?
Analytic functions are computed after all joins, WHERE clause, GROUP BY and HAVING are
computed on the query. The main ORDER BY clause of the query operates after the analytic
functions. So analytic functions can only appear in the select list and in the main ORDER BY clause of
the query.
In absence of any PARTITION or <window_clause> inside the OVER( ) portion, the function acts on
entire record set returned by the where clause.
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Analytic Functions(order-by-clause)
• The order_by_clause is used to order rows, or siblings, within a partition. So if an
analytic function is sensitive to the order of the siblings in a partition you should
include an order_by_clause.
• ORDER BY <sql_expr> [ASC or DESC] NULLS [FIRST or LAST]
• The functions SUM, COUNT, AVG, MIN, MAX are the common analytic functions the
result of which does not depend on the order of the records.
• Functions like LEAD, LAG, RANK, DENSE_RANK, ROW_NUMBER, FIRST, FIRST
VALUE, LAST, LAST VALUE depends on order of records.
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ROW_NUMBER, RANK and DENSE_RANK
All the above three functions assign integer
values to the rows depending on their order.
ROW_NUMBER( ) gives a running serial number
to a partition of records. It is very useful in
reporting, especially in places where different
partitions have their own serial numbers.
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ROW_NUMBER, RANK and DENSE_RANK
RANK and DENSE_RANK both provide rank to
the records based on some column value or
expression. In case of a tie of 2 records at
position N, RANK declares 2 positions N and
skips position N+1 and gives position N+2 to the
next record. While DENSE_RANK declares 2
positions N but does not skip position N+1.
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LEAD and LAG
LEAD has the ability to compute an expression on the next rows (rows which are going to
come after the current row) and return the value to the current row.
• Syntax
LEAD (<sql_expr>, <offset>, <default>) OVER (<analytic_clause>)
<sql_expr> is the expression to compute from the leading row.
<offset> is the index of the leading row relative to the current row.
<offset> is a positive integer with default 1.
<default> is the value to return if the <offset> points to a row outside the partition range.
The syntax of LAG is similar except that the offset for LAG goes into the previous rows.
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FIRST VALUE and LAST VALUE function
• Syntax
FIRST_VALUE(<sql_expr>) OVER
(<analytic_clause>)
The FIRST_VALUE analytic function picks the
first record from the partition after doing the
ORDER BY.
The <sql_expr> is computed on the columns of
this first record and results are returned.
The LAST_VALUE function is used in similar
context except that it acts on the last record of
the partition.
How many days after the first hire of each department were
the next employees hired?
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FIRST and LAST function
The FIRST function (or more properly KEEP FIRST function) is used in a very special situation.
Suppose we rank a group of record and found several records in the first rank. Now we want to apply
an aggregate function on the records of the first rank. KEEP FIRST enables that.
• syntax
Function( ) KEEP (DENSE_RANK FIRST ORDER BY <expr>) OVER (<partitioning_clause>)
Please note that FIRST and LAST are the only functions that deviate from the general syntax of
analytic functions. They do not have the ORDER BY inside the OVER clause. Neither do they support
any <window> clause. The ranking done in FIRST and LAST is always DENSE_RANK.
The LAST function is used in similar context to perform computations on last ranked records.
How each employee's salary compare with the average salary of the first year hires of their department?
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Analytic Functions(window-clause)
• This group of rows is known as a window, which is why analytic functions are
sometimes referred to as window[ing] functions.
• We have seen previously the query_partition_clause controls the window, or group of
rows, the analytic operates on. The windowing_clause gives some analytic functions
a further degree of control over this window within the current partition. The
windowing_clause is an extension of the order_by_clause and as such, it can only be
used if an order_by_clause is present.
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<window_clause>
• [ROW or RANGE] BETWEEN <start_expr> AND <end_expr>
<start_expr> can be any one of the following
• UNBOUNDED PRECEDING
• CURRENT ROW
• <sql_expr> PRECEDING or FOLLOWING.
<end_expr> can be any one of the following
• UNBOUNDED FOLLOWING
• CURRENT ROW
• <sql_expr> PRECEDING or FOLLOWING.
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• For ROW type windows the definition is in terms of row numbers before or after the
current row. So for ROW type windows <sql_expr> must evaluate to a positive
integer.
• For RANGE type windows the definition is in terms of values before or after the
current ORDER.
• The ROW or RANGE window cannot appear together in one OVER clause.
• The window clause is defined in terms of the current row. But may or may not include
the current row.
• The start point of the window and the end point of the window can finish before the
current row or after the current row.
• Only start point cannot come after the end point of the window.
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LISTAGG Function
• Description
The Oracle/PLSQL LISTAGG function concatenates values of the
measure_column for each GROUP based on the order_by_clause.
• SYNTAX
LISTAGG (measure_column [, 'delimiter']) WITHIN GROUP (order_by_clause)
[OVER (query_partition_clause)]
• measure_column
The column whose values you wish to concatenate together in the result set.
Null values in the measure_column are ignored.
• Delimiter
Optional. It is the delimiter to use when separating the measure_column values
when outputting the results.
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LISTAGG Function
• order_by_clause
It determines the order that the concatenated values (ie: measure_column) are
returned.
• Example
SELECT LISTAGG(product_name, ', ') WITHIN GROUP (ORDER BY product_name)
"Product_Listing" FROM products;
Product_id Product_name
1001 Bananas
1002 Apples
1003 Pears
1004 Oranges
Product_Listing
Apples, Bananas, Oranges, Pears
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TRANSLATE Function
• Description
The Oracle/PLSQL TRANSLATE function replaces a sequence of characters in
a string with another set of characters. However, it replaces a single character
at a time.
For example, it will replace the 1st character in the string_to_replace with the
1st character in the replacement_string. Then it will replace the 2nd character
in the string_to_replace with the 2nd character in the replacement_string, and
so on.
• Syntax
TRANSLATE( string1, string_to_replace, replacement_string )
• string1
The string to replace a sequence of characters with another set of characters.
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TRANSLATE Function
• string_to_replace
The string that will be searched for in string1.
• replacement_string
All characters in the string_to_replace will be replaced with the corresponding
character in the replacement_string.
• Example
TRANSLATE('1tech23', '123', '456') Result: '4tech56'
TRANSLATE('222tech', '2ec', '3it') Result: '333tith'
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• Description
The Oracle REGEXP_LIKE condition allows you to perform regular expression
matching in the WHERE clause of a SELECT, INSERT, UPDATE, or DELETE
statement.
• SYNTAX
REGEXP_LIKE ( expression, pattern [, match_parameter ] )
• Expression
A character expression such as a column or field. It can be a
VARCHAR2, CHAR, NVARCHAR2, NCHAR, CLOB or NCLOB data type.
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• Pattern
The regular expression matching information.
^ Matches the beginning of a string.
$ Matches the end of a string.
* Matches zero or more occurrences.
| Used like an "OR" to specify more than one alternative.
+ Matches one of more occurrences.
? Matches zero or one occurrence.
. Matches any character except NULL.
[ ] Used to specify a matching list where you are trying to match any one of the characters in the
list.
[^ ] Used to specify a nonmatching list where you are trying to match any character except for the
ones in the list.
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• match_parameter
Optional. It allows you to modify the matching behavior for the REGEXP_LIKE
condition.
• Example
SELECT last_name FROM contacts WHERE REGEXP_LIKE (last_name, 'Anders(o|e|a)n');
SELECT last_name FROM contacts WHERE REGEXP_LIKE (last_name, '^A(*)');
SELECT last_name FROM contacts WHERE REGEXP_LIKE (last_name, '(*)n$');
‘c’ Perform case-sensitive matching.
‘i’ Perform case-insensitive matching.
‘n’ Allows the period character (.) to match the newline character.
‘m’ expression is assumed to have multiple lines, where ^ is the start of a line and $ is the end
of a line, regardless of the position of those characters in expression.
‘x’ Whitespace characters are ignored.
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• Description
The Oracle/PLSQL REGEXP_COUNT function counts the number of times that
a pattern occurs in a string.
• Syntax
REGEXP_COUNT( string, pattern [, start_position [, match_parameter ] ] )
• string
The string to search. string can be CHAR, VARCHAR2, NCHAR,
NVARCHAR2, CLOB, or NCLOB.
• pattern
The regular expression matching information.
• start_position
Optional. It is the position in string where the search will start. If omitted, it
defaults to 1 which is the first position in the string.
• match_parameter
Optional. It allows you to modify the matching behavior for the
REGEXP_COUNT function.
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• Example
SELECT REGEXP_COUNT ('TechOnTheNet is a great resource!', 't') FROM dual;
Result: 2.
SELECT REGEXP_COUNT ('TechOnTheNet is a great resource!', 't', 1, 'i') FROM dual;
Result: 4
SELECT REGEXP_COUNT ('The example shows how to use the REGEXP_COUNT function.', 'the',
4, 'i') FROM dual;
Result: 1
SELECT REGEXP_COUNT ('Anderson', 'a|e|i|o|u') FROM dual;
Result: 2
SELECT REGEXP_COUNT ('Anderson', 'a|e|i|o|u', 1, 'i') FROM dual;
Result: 3
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COALESCE Function
• Description
The Oracle/PLSQL COALESCE function returns the first non-null expression in
the list. If all expressions evaluate to null, then the COALESCE function will
return null.
• Syntax
COALESCE( expr1, expr2, ... expr_n )
• expr1, expr2, ... expr_n
The expressions to test for non-null values.
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COALESCE Function
• Example
SELECT COALESCE( address1, address2, address3 ) result FROM suppliers;
The above COALESCE function is equivalent to the following IF-THEN-ELSE statement:
IF address1 is not null THEN
result := address1;
ELSIF address2 is not null THEN
result := address2;
ELSIF address3 is not null THEN
result := address3;
ELSE
result := null;
END IF;
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EXTRACT Function
• Description
The Oracle/PLSQL EXTRACT function extracts a value from a date or interval
value.
• Syntax
EXTRACT ( { YEAR | MONTH | DAY | HOUR | MINUTE | SECOND } | {
TIMEZONE_HOUR | TIMEZONE_MINUTE } | { TIMEZONE_REGION |
TIMEZONE_ABBR } FROM { date_value | interval_value } )
• Example
EXTRACT(YEAR FROM DATE '2003-08-22') Result: 2003
EXTRACT(MONTH FROM DATE '2003-08-22') Result: 8
EXTRACT(DAY FROM DATE '2003-08-22') Result: 22
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ADD_MONTHS Function
• Description
The Oracle/PLSQL ADD_MONTHS function returns a date with a specified
number of months added.
• Syntax
ADD_MONTHS( date1, number_months )
• Date1
The starting date (before the n months have been added).
• number_months
The number of months to add to date1.
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ADD_MONTHS Function
• Example
ADD_MONTHS('01-Aug-03', 3)
Result: '01-Nov-03‘
ADD_MONTHS('01-Aug-03', -3)
Result: '01-May-03'
ADD_MONTHS('21-Aug-03', -3)
Result: '21-May-03'
ADD_MONTHS('31-Jan-03', 1)
Result: '28-Feb-03'
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INITCAP Function
• Description
The Oracle/PLSQL INITCAP function sets the first character in each word to uppercase
and the rest to lowercase.
• Syntax
INITCAP( string1 )
• string1
The string argument whose first character in each word will be converted to uppercase and
all remaining characters converted to lowercase.
• Example
INITCAP('tech on the net');
Result: 'Tech On The Net‘
INITCAP('GEORGE BURNS');
Result: 'George Burns'
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INSTR Function
• Description
The Oracle/PLSQL INSTR function returns the location of a substring in a
string.
• Syntax
INSTR( string, substring [, start_position [, nth_appearance ] ] )
• String
The string to search. string can be CHAR, VARCHAR2, NCHAR,
NVARCHAR2, CLOB, or NCLOB.
• Substring
The substring to search for in string. substring can be CHAR, VARCHAR2,
NCHAR, NVARCHAR2, CLOB, or NCLOB.
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INSTR Function
• start_position
Optional. The position in string where the search will start. If omitted, it defaults
to 1. The first position in the string is 1. If the start_position is negative, the
INSTR function counts back start_position number of characters from the end
of string and then searches towards the beginning of string.
• nth_appearance
Optional. The nth appearance of substring. If omitted, it defaults to 1.
Note: If substring is not found in string, then the INSTR function will return 0.
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INSTR Function
• Example
INSTR('Tech on the net', 'e') Result: 2 (the first occurrence of 'e')
INSTR('Tech on the net', 'e', 1, 1) Result: 2 (the first occurrence of 'e')
INSTR('Tech on the net', 'e', 1, 2) Result: 11 (the second occurrence of 'e')
INSTR('Tech on the net', 'e', 1, 3) Result: 14 (the third occurrence of 'e')
INSTR('Tech on the net', 'e', -3, 2) Result: 2
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GREATEST Function
• Description
The Oracle/PLSQL GREATEST function returns the greatest value in a list of
expressions.
• Syntax
GREATEST( expr1 [, expr2, ... expr_n] )
• expr1
The first expression to be evaluated whether it is the greatest.
• expr2, ... expr_n
Optional. Additional expressions that are to be evaluated.
Note:
If the datatypes of the expressions are different, all expressions will be converted to
whatever datatype expr1 is.
If the comparison is based on a character comparison, one character is considered greater
than another if it has a higher character set value.
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GREATEST Function
• Example
GREATEST(2, 5, 12, 3) Result: 12
GREATEST('2', '5', '12', '3') Result: '5'
GREATEST('apples', 'oranges', 'bananas') Result: 'oranges'
GREATEST('apples', 'applis', 'applas') Result: 'applis'
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Name of Functions
select distinct
object_name
from
all_arguments
where
package_name = 'STANDARD';
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Advanced functions in PL SQL

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