revDataFromQuery

Type

function

Summary

Gets records from a database according to a SQL query and places the resulting data in a variable, without creating a record set.

Syntax

revDataFromQuery([<columnDelim>],[<rowDelim>], <databaseID>, <SQLQuery> [, <varsList>])

Description

Use the revDataFromQuery function when you want to use or display data from a database, but not continue to work with the records that contain it.

It is convenient to use the revDataFromQuery function, instead of revQueryDatabase, when you want to obtain the data for use but don't need to retain a reference to the records that the data came from. The revDataFromQuery function executes the SQLQuery, gets the records found by the query, closes the record set created by the query, and returns the data.

Important

: The revDataFromQuery function should not be used if any of the data being retrieved is binary, doing so will probably produce unexpected results. If you wish to use this function to return things like image data, the data should be encoded before being stored in the database, this could for example be done with the base64Encode function. Also remember to specify a columDelim and rowDelim that will not appear in the data. Alternatively, both these problems can be avoided by using the revQueryDatabase function to generate a record set, then using revDatabaseColumnNamed to retrieve each field individually.

The SQLQuery may contain one or more placeholders, which are sequential numbers prepended by a colon. The revDataFromQuery function substitutes the corresponding variable name in the variablesList for each of these placeholders. For example, if you have two variables called "valueX" and "valueY", you can use a SQLQuery that includes placeholders as follows:

    get revDataFromQuery(, , myID, \"SELECT x,y FROM test \" && \
    \"WHERE x = :1 AND y = :2\", \"valueX\", \"valueY\" )

The content of the variable valueX is substituted for the ":1" in the SQLQuery (in both places where ":1" appears), and the content of valueY is substituted for ":2".

To pass binary data in a variable in the variablesList, prepend \"*b\" to the variable name. The revDataFromQuery function strips the binary marker \"*b\" and passes it to the database as binary data, rather than text data.

    local tImageData
    put the text of image \"MyImage\" into tImageData
    get revDataFromQuery(, , myID, \
    \"SELECT size FROM images WHERE imagedata = :1\", \"*btImageData\" )

You can also use the name of a numerically indexed array, instead of a list of variable names. In this case, the elements of the array are substituted for the corresponding placeholders. To pass binary data in an array element, prepend \"*b\" to the element's value.

    local tImageDataArray
    put \"*b\" & the text of image \"MyImage\" into tImageDataArray[1]
    get revDataFromQuery(, , myId, \
    \"SELECT size FROM images WHERE imagedata = :1\", \"tImageDataArray\" )

To pass an asterisk as part of the query, substitute a percent sign (%). For example, to use the query \"SELECT * FROM Customers WHERE Cust.Name Like \'*Inc.\'\", use a statement like the following:

    get revDataFromQuery(2, \
    \"SELECT * FROM Customers WHERE Cust.Name Like \'%Inc.\'\" )

If the query is not successful, the revDataFromQuery function returns an error message beginning with the string "revdberr,". You can test for success by checking whether the first item of the returned value is "revdberr".

Important

The revDataFromQuery function is part of the Database library. To ensure that the function works in a standalone application, you must include this custom library when you create your standalone. In the Inclusions pane of the Standalone Application Settings window, make sure both the "Database" library checkbox and those of the database drivers you are using are checked.

Parameters

Name	Type	Description
columnDelim		A character, or an expression that evaluates to a character. If no columnDelim is specified, columns are delimited by the tab character.
rowDelim		A character, or an expression that evaluates to a character. If no rowDelim is specified, rows are delimited by the return character.
databaseID		The number returned by the revOpenDatabase function when the database was opened.
SQLQuery	string	A string in Structured Query Language.
varsList		The varsList consists of one or more variable names (or expressions that evaluate to variable names), separated by commas. The variable names may also be array elements.

Examples

revDataFromQuery(, , tConnectionId, the text of field "Query")

get revDataFromQuery(comma, return, tConnectionId, tQuery)

get revDataFromQuery(tab, return, tConnectionId, \
"SELECT * FROM myTable WHERE id = :1", "tCustomerDetails[id]")

Related

command: revCloseCursor, revExecuteSQL

control structure: function

function: base64Encode, revQueryDatabase, revDatabaseColumnNamed

glossary: function, LiveCode custom library, return, variable, database, record set, record, Standalone Application Settings, standalone application, SQL query, delimit, prepend

keyword: string

library: Database library

Compatibility and Support

Introduced

LiveCode 1.1.1

OS

mac

windows

linux

ios

android

Platforms

desktop

server

mobile