Prefix Queries with LIKE and NOT LIKE in Java

Printer QR-Code in Java Prefix Queries with LIKE and NOT LIKE
Prefix Queries with LIKE and NOT LIKE
Quick Response Code Maker In Java
Using Barcode maker for Java Control to generate, create QR Code ISO/IEC18004 image in Java applications.
The LIKE operator enables you to perform substring text matching as part of a query When using LIKE, the percent sign (%) is the wildcard characterTo do a prefix search, put the prefix constant followed by the percent sign within single quotes:
Barcode Maker In Java
Using Barcode printer for Java Control to generate, create barcode image in Java applications.
WHERE name LIKE 'Wil%'
Bar Code Decoder In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
You can also place the wildcard character at the beginning:
QR-Code Printer In C#.NET
Using Barcode generator for VS .NET Control to generate, create QR Code 2d barcode image in VS .NET applications.
WHERE name LIKE '%Smith'
QR Generation In .NET Framework
Using Barcode creation for ASP.NET Control to generate, create Denso QR Bar Code image in ASP.NET applications.
Finally, it can be placed at both the beginning and the end:
Generate QR-Code In .NET
Using Barcode printer for VS .NET Control to generate, create QR Code ISO/IEC18004 image in VS .NET applications.
WHERE name LIKE '%son%'
QR Code Encoder In VB.NET
Using Barcode creation for .NET Control to generate, create QR Code JIS X 0510 image in .NET applications.
Placing the wildcard at the beginning will circumvent the index and potentially require a table scanThis is an expensive operation, so combining it with other selective comparisons is advised
Bar Code Generation In Java
Using Barcode generator for Java Control to generate, create barcode image in Java applications.
4 A Closer Look at Select
UCC - 12 Printer In Java
Using Barcode creator for Java Control to generate, create EAN / UCC - 13 image in Java applications.
You can use the NOT LIKE operator to match values that do not contain the specified constantThe usage is the same as LIKE:
Barcode Creator In Java
Using Barcode drawer for Java Control to generate, create barcode image in Java applications.
WHERE name NOT LIKE 'Wil%' WHERE name NOT LIKE '%Smith' WHERE name NOT LIKE '%son%'
Encoding GTIN - 13 In Java
Using Barcode creation for Java Control to generate, create EAN-13 Supplement 5 image in Java applications.
IS NULL and IS NOT NULL
Data Matrix ECC200 Printer In Java
Using Barcode generator for Java Control to generate, create Data Matrix image in Java applications.
Testing for the existence of an attribute within an item can be an important condition, and the IS NOT NULL operator enables you to do itThis operator takes a single attribute name on the left side:
Code 2 Of 5 Generator In Java
Using Barcode generator for Java Control to generate, create Standard 2 of 5 image in Java applications.
SELECT * FROM users WHERE `email-confirmation` IS NOT NULL
Paint Barcode In .NET
Using Barcode creation for VS .NET Control to generate, create bar code image in .NET framework applications.
The IS
Drawing ANSI/AIM Code 39 In .NET Framework
Using Barcode creator for ASP.NET Control to generate, create Code 39 Full ASCII image in ASP.NET applications.
NULL
Make Bar Code In .NET Framework
Using Barcode creation for .NET framework Control to generate, create bar code image in Visual Studio .NET applications.
operator matches items where no value exists for the named attribute:
DataMatrix Creation In C#
Using Barcode generation for Visual Studio .NET Control to generate, create Data Matrix image in Visual Studio .NET applications.
SELECT * FROM users WHERE `email-confirmation` IS NULL
Generate GS1 128 In .NET
Using Barcode drawer for VS .NET Control to generate, create UCC.EAN - 128 image in Visual Studio .NET applications.
A common use for IS NOT NULL, beyond the need to find values that exist, is to meet the requirement of the WHERE clause to ensure that the sort attribute exists in all matching rows:
Data Matrix 2d Barcode Reader In Visual Studio .NET
Using Barcode scanner for .NET framework Control to read, scan read, scan image in Visual Studio .NET applications.
SELECT * FROM users ORDER BY `date-created`
USS Code 39 Creation In VB.NET
Using Barcode printer for Visual Studio .NET Control to generate, create Code-39 image in VS .NET applications.
This Select returns an InvalidQueryExpression error because you cannot sort on an attribute that might not exist in the result setThe easiest way to ensure existence is add an IS NOT NULL test, as follows:
SELECT * FROM users WHERE `date-created` IS NOT NULL ORDER BY `date-created`
Multi-Valued Attribute Queries
An important consideration overlooked thus far is what is going to happen with these comparisons for attributes with multiple valuesThe answer to this question is that each attribute value is considered individually Given the function of the operators as discussed so far, considering each attribute individually might seem to be problematic It is very possible to construct queries where every item with a multi-valued attribute is returned For example:
SELECT * FROM products WHERE count != '100'
Every item with more than one value for the count attribute will end up matching this comparison because each value is required to be unique, therefore at least one value must be something other than 100 It is just as easy to construct a query that is guaranteed to match none of the items with multiple values For example, consider that the products domain has multi-valued attribute named size containing the available sizes
Multi-Valued Attribute Queries
for the productA query to find products that come in both medium and small might look like this:
SELECT * FROM products WHERE size = 'S' AND size = 'M'
The preceding query can never return any values because both comparisons are evaluated together as a single predicate against each value Beyond the mere avoidance of these problems, it is necessary to have a way to isolate the individual values of a multi-valued attribute for comparison purposesThe SimpleDB query language defines two constructs to fill this role: the INTERSECTION operator and the EVERY() function
Multiple Predicate Queries with the INTERSECTION Operator
To illustrate the difference between the single predicate queries demonstrated so far and multiple predicate queries, here is an example scenario Consider a data set where each item in the domain is the bookmark of a user One of the attributes stored with a bookmark is tagTag can hold multiple values as defined by the userThis is the query to get bookmarks with a specific tag for instance, css :
SELECT * FROM bookmarks WHERE tag = 'css'
This works as expected for both items with a single tag attribute set to css, as well as items with many tag values, one of which is css You can run into problems when selecting for bookmarks tagged with two specific tags, though:
SELECT * FROM bookmarks WHERE tag = 'css' AND tag = 'html'
This does not work, and is actually guaranteed to always return no resultsThe reason has to do with the way SimpleDB executes queriesThis query, as well as each of the queries shown so far, is a single predicate queryThe behavior of the single predicate is as if all of the conditions are combined into exactly one matching expression for each attribute in the queryThese expressions are then compared against each value individually In the case of the preceding tag query, the two conditions = 'css' and = 'html' are applied together to each value of the tag attribute Because no value can equal both css and html, the query always returns empty To solve this problem and apply criteria separately to multiple attribute values, the INTERSECTION operator enables the definition of multiple predicatesTo adjust the previous example:
SELECT * FROM bookmarks WHERE tag = 'css' INTERSECTION tag = 'html'
Now, instead of two comparisons combined into a single predicate, two separate predicates are createdThe behavior of INTERSECTION is as if each predicate is run as a separate query in isolation and then only those items appearing in the results of both predicates are returnedThe limit on the number of predicates is 20 Dividing a query into predicates with the INTERSECTION operator is mainly useful for selecting attributes with multiple valuesAlthough INTERSECTION can also be used with