Hướng dẫn dùng mysql tableau trong PHP

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Why use string functions
String functions available in Tableau:
Create a string calculation

This article introduces string functions and their uses in Tableau. It also demonstrates how to create a string calculation using an example.

Why use string functions

String functions allow you to manipulate string data (i.e. data made of text). Tableau uses the current International Components for Unicode (ICU) library when comparing strings. The way strings are sorted and compared is based both on language and locale, and it’s possible for vizzes to change as the ICU is continuously updated for better language support.

For example, you might have a field that contains all of your customers' first and last names. One member might be: Jane Johnson. You can pull the last names from all your customers into a new field using a string function.

The calculation might look something like this:

SPLIT([Customer Name], ' ', 2)

Therefore, SPLIT('Jane Johnson' , ' ', 2) = 'Johnson'.

String functions available in Tableau:

Function

Syntax

Definition

ASCII

ASCII(string)

Returns the ASCII code for the first character of string.

Example:

ASCII('A') = 65

CHAR

CHAR(number)

Returns the character encoded by the ASCII code number.

Example:

CHAR(65) = 'A'

CONTAINS

CONTAINS(string, substring)

Returns true if the given string contains the specified substring.

Example:

CONTAINS(“Calculation”, “alcu”) = true

ENDSWITH

ENDSWITH(string, substring)

Returns true if the given string ends with the specified substring. Trailing white spaces are ignored.

Example:

ENDSWITH(“Tableau”, “leau”) = true

FIND

FIND(string, substring, [start])

Returns the index position of substring in string, or 0 if the substring isn't found. If the optional argument start is added, the function ignores any instances of substring that appear before the index position start. The first character in the string is position 1.

Examples:

FIND("Calculation", "alcu") = 2
FIND("Calculation", "Computer") = 0
FIND("Calculation", "a", 3) = 7
FIND("Calculation", "a", 2) = 2
FIND("Calculation", "a", 8) = 0
FIND("Calculation", "a", 3) = 7
FIND("Calculation", "a", 2) = 2
FIND("Calculation", "a", 8) = 0

FINDNTH

FINDNTH(string, substring, occurrence)

Returns the position of the nth occurrence of substring within the specified string, where n is defined by the occurrence argument.

Note: FINDNTH is not available for all data sources.

Example:

FINDNTH("Calculation", "a", 2) = 7

LEFT

LEFT(string, number)

Returns the left-most number of characters in the string.

Example:

LEFT("Matador", 4) = "Mata"

LEN

LEN(string)

Returns the length of the string.

Example:

LEN("Matador") = 7

LOWER

LOWER(string)

Returns string, with all characters lowercase.

Example:

LOWER("ProductVersion") = "productversion"

LTRIM

LTRIM(string)

Returns the string with any leading spaces removed.

Example:

LTRIM(" Matador ") = "Matador "

MAX

MAX(a, b)

Returns the maximum of a and b (which must be of the same type). This function is usually used to compare numbers, but also works on strings. With strings, MAX finds the value that is highest in the sort sequence defined by the database for that column. It returns Null if either argument is Null.

Example:

MAX ("Apple","Banana") = "Banana"

MID

(MID(string, start, [length])

Returns the string starting at index position start. The first character in the string is position 1. If the optional argument length is added, the returned string includes only that number of characters.

Examples:

MID("Calculation", 2) = "alculation"
MID("Calculation", 2, 5) ="alcul"

MIN

MIN(a, b)

Returns the minimum of a and b (which must be of the same type). This function is usually used to compare numbers, but also works on strings. With strings, MIN finds the value that is lowest in the sort sequence. It returns Null if either argument is Null.

Example:

MIN ("Apple","Banana") = "Apple"

REPLACE

REPLACE(string, substring, replacement)

Searches string for substring and replaces it with replacement. If substring is not found, the string is not changed.

Example:

REPLACE("Version8.5", "8.5", "9.0") = "Version9.0"

RIGHT

RIGHT(string, number)

Returns the right-most number of characters in string.

Example:

RIGHT("Calculation", 4) = "tion"

RTRIM

RTRIM(string)

Returns string with any trailing spaces removed.

Example:

RTRIM(" Calculation ") = " Calculation"

SPACE

SPACE(number)

Returns a string that is composed of the specified number of repeated spaces.

Example:

SPACE(1) = " "

SPLIT

SPLIT(string, delimiter, token number)

Returns a substring from a string, using a delimiter character to divide the string into a sequence of tokens.

The string is interpreted as an alternating sequence of delimiters and tokens. So for the string abc-defgh-i-jkl, where the delimiter character is ‘-‘, the tokens are abc, defgh, i, and jlk. Think of these as tokens 1 through 4. SPLIT returns the token corresponding to the token number. When the token number is positive, tokens are counted starting from the left end of the string; when the token number is negative, tokens are counted starting from the right.

Examples:

SPLIT (‘a-b-c-d’, ‘-‘, 2) = ‘b’
SPLIT (‘a|b|c|d’, ‘|‘, -2) = ‘c’

Note: The split and custom split commands are available for the following data sources types: Tableau data extracts, Microsoft Excel, Text File, PDF File, Salesforce, OData, Microsoft Azure Market Place, Google Analytics, Vertica, Oracle, MySQL, PostgreSQL, Teradata, Amazon Redshift, Aster Data, Google Big Query, Cloudera Hadoop Hive, Hortonworks Hive, and Microsoft SQL Server.

Some data sources impose limits on splitting string. The following table shows which data sources support negative token numbers (splitting from the right) and whether there is a limit on the number of splits allow per data source. A SPLIT function that specifies a negative token number and would be legal with other data sources will return this error with these data sources: “Splitting from right is not support by the data source.”

Data Source	Left/Right Constraints	Maximum Number of Splits	Version limitations
Tableau Data Extract	Both	Infinite
Microsoft Excel	Both	Infinite
Text file	Both	Infinite
Salesforce	Both	Infinite
OData	Both	Infinite
Google Analytics	Both	Infinite
Tableau Data Server	Both	Infinite	Supported in version 9.0.
Vertica	Left only	10
Oracle	Left only	10
MySQL	Both	10
PostgreSQL	Left only prior to version 9.0; both for version 9.0 and above	10
Teradata	Left only	10	Version 14 and later
Amazon Redshift	Left only	10
Aster Database	Left only	10
Google BigQuery	Left only	10
Hortonworks Hadoop Hive	Left only	10
Cloudera Hadoop	Left only	10	Impala supported starting in version 2.3.0.
Microsoft SQL Server	Both	10	2008 and later

STARTSWITH

STARTSWITH(string, substring)

Returns true if string starts with substring. Leading white spaces are ignored.

Example:

STARTSWITH(“Joker”, “Jo”) = true

TRIM

TRIM(string)

Returns the string with leading and trailing spaces removed.

Example:

TRIM(" Calculation ") = "Calculation"

UPPER

UPPER(string)

Returns string, with all characters uppercase.

Example:

UPPER("Calculation") = "CALCULATION"

Create a string calculation

Follow along with the steps below to learn how to create a string calculation.

In Tableau Desktop, connect to the Sample - Superstore saved data source, which comes with Tableau.
Navigate to a worksheet.
From the Data pane, under Dimensions, drag Order ID to the Rows shelf.
Notice that every order ID contains values for country (CA and US, for example), year (2011), and order number (100006). For this example, you will create a calculation to pull only the order number from the field.
Select Analysis > Create Calculated Field.
In the calculation editor that opens, do the following:

Name the calculated field Order ID Numbers.
Enter the following formula:
RIGHT([Order ID], 6)
This formula takes the specified digits (6) from the right of the string and pulls them into a new field.
Therefore, RIGHT('CA-2011-100006' , 6) = '100006'.
When finished, click OK.
The new calculated field appears under Dimensions in the Data pane. Just like your other fields, you can use it in one or more visualizations.

From the Data pane, drag Order ID Numbers to the Rows shelf. Place it to the right of Order ID.
Notice how the fields differ now.

Hướng dẫn dùng mysql tableau trong PHP

Why use string functions

String functions available in Tableau:

Function

Syntax

Definition

Create a string calculation

See Also

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