Topics on Filtering Records
Topics on Filtering Records
Other Topics on Filtering
Hiding a Column
In our SELECT statements so far, we were selecting the columns we needed to display. When formulating such a statement, you can apply a condition to a column without including that column in the result.
For example, consider a query used to display a list of female students. Since we know that the result would show only the girls, it becomes redundant to include the Gender column in the statement. In this case, you can hide that column in the result. To visually hide a column from a query, in the Criteria pane, set the condition expression in its corresponding Filter box. Then click the check box of Outpu to remove it. To hide a field in SQL, omit that column in the SELECT statement but involve it in the WHERE condition. Here is an example: SELECT DateOfBirth, LastName,
FirstName, State, ParentsNames
FROM Registration.Students
WHERE Gender = N'Female';
GO
This would produce:
Notice that the SELECT statement doesn't have the Gender column and the resulting query doesn't show the Gender column.
Consider the following Employees table: CREATE DATABASE Corporation;
GO
USE Corporation;
GO
CREATE TABLE Employees
(
EmployeeNumber int unique not null,
FirstName nvarchar(20),
LastName nvarchar(20) not null,
Department nvarchar(50) null,
EmploymentStatus nvarchar(30),
HourlySalary money
);
GO
INSERT INTO Employees
VALUES(84628, N'Anthony', N'Holms', N'Corporate', N'Full Time', 24.72),
(40574, N'William', N'Wilson', N'Information Technology', N'Full Time', 21.18),
(27462, N'Peter', N'Swanson', N'Corporate', N'Full Time', 22.84),
(52835, N'Edward', N'Johansen', N'Information Technology',N'Consultant',15.50),
(93075, N'Sharon', N'Edson', N'Accounting', N'Full Time', 28.74),
(82718, N'Yanuh', N'Hadhah', N'Corporate', N'Full Time', 14.86),
(29174, N'Hamin', N'Souleyman', N'Public Relations', N'Consultant', 18.76);
GO
You can use all or some records from an existing table to create a new table that would contain those existing records. To do this, use the following formula: SELECT Columns INTO NewTableName FROM ExistingTable [WHERE Condition] To use all columns and all records, start with the SELECT operator, followed by *, followed by INTO, followed by a name for the table you want to create, followed by FROM, and the name of the original table that contains the records. Here is an example: USE Corporation; GO SELECT * INTO CompanyRecipients FROM Employees; GO Instead of using all columns, you can specify only the desired columns after the SELECT keyword. Here is an example: USE Corporation; GO SELECT EmployeeNumber, LastName, FirstName, EmploymentStatus INTO Salaried FROM Employees; GO Instead of using all records, you can use a condition by which the records would be selected and added to the new table you are creating. To set the condition, you can create a WHERE statement as the last in the whole expression. Here is an example: USE Corporation; GO SELECT * INTO FullTimeEmployees FROM Employees WHERE EmploymentStatus = N'Full Time'; GO
Most or all of the criteria we have specified with the WHERE keyword had to exactly match the specified criterion. In some cases, you may not remember the exact value of records but you want to specify some type of approximation. To do this, you use the LIKE operator.
The most fundamental comparison performed on a string-based field is to find out whether it is equal to a certain string. We know that this operation can be performed using the = operator. Here is an example: SELECT FirstName, LastName, Gender, [State], ParentsNames FROM Registration.Students WHERE State = N'VA'; GO The LIKE operator can be used to perform the same operation. To do this, use the following formula: WHERE ColumnName LIKE Value In this case, the name of the column is used as the Expression and the string in the field is the pattern. Here is an example: SELECT FirstName, LastName, Gender, [State], ParentsNames FROM Registration.Students WHERE State LIKE N'VA'; GO This and the previous code produce the same result:
To make the operation easier to read, you can put it in parentheses. The above code can be written as follows: SELECT FirstName, LastName, Gender, [State], ParentsNames FROM Registration.Students WHERE (State LIKE N'VA'); GO
As done with all Boolean operations, there are ways you can negate a LIKE operation. Probably the easiest way to negate a LIKE operation is to precede the Expression with the NOT operator. Here is an example: SELECT FirstName, LastName,
Gender, State, ParentsNames
FROM Registration.Students
WHERE NOT State LIKE N'VA';
GO
If you precede the expression with NOT, it is recommended that you put the section after NOT between parentheses. Here is an example: SELECT FirstName, LastName, Gender, [State], ParentsNames FROM Registration.Students WHERE NOT (State LIKE N'VA'); GO As an alternative, in most cases, you can also precede the LIKE keyword with NOT. Here is an example:
This formula would produce the same result as the previous one:
You can also negate a negation. Here is an example: SELECT FirstName, LastName,
Gender, [State], ParentsNames
FROM Registration.Students
WHERE NOT State NOT LIKE N'VA';
GO
This is the same as: SELECT FirstName, LastName, Gender, [State], ParentsNames FROM Registration.Students WHERE NOT (State NOT LIKE N'VA'); GO If you negate a negation, you can get the result as you none of both negations was used.
Matching Any Character The idea of using a LIKE operator is to give an approximation of the value you want to compare to a field. To formulate this approximation, you use wildcards combined with the LIKE operator. If you want to match any character, in any combination, for any length, use the % wildcard. If you precede it with a letter, as in S%, the condition would consist of finding any string that starts with S. Imagine that you want to get a list of students whose last names start with S. You would type the condition as LIKE 'S%'. To do this visually, in the Criteria pane, under the Filter column, type the condition. Here is an example:
This would produce:
You can negate this condition by preceding it with NOT. Here is an example: SELECT FirstName [First Name], LastName "Last Name", Gender, [State], ParentsNames [Parents Names] FROM Registration.Students WHERE NOT (LastName LIKE N'S%') This would produce:
This time, the result is the list of students whose last names don't start with S.
When you precede the % character with a letter, only that letter would be considered. Alternatively, you can specify a group of characters, called a sub-string, that would precede the % symbol. For example, if you have some first names that start with Ch in a list but you don't remember the end of the name you are looking for, to create the list, you can specify that the first name would start with Ch and end with whatever. In this case, you would use Ch% as follows: SELECT FirstName [First Name], LastName "Last Name", Gender, [State], SingleParentHome "Single Parent Home?" FROM Registration.Students WHERE LastName LIKE N'Ch%'; GO This would produce:
Instead of ending a letter or a group of letters with %, you can begin the LIKE statement with %. An example would be LIKE "%son". In this case, all strings that end with son, such as Johnson or Colson, would be considered. If you remember neither the beginning nor the end of a string you want to search for, but you know a sub-string that is probably included in the type of string you are looking for, you can precede it with % and end it with %. An example would be LIKE "%an%". In this case, all strings that include "an" anywhere inside would be considered. Here is an example: SELECT FirstName [First Name], LastName "Last Name", Gender, [State], CASE SingleParentHome WHEN 1 THEN N'Yes' WHEN 0 THEN N'No' ELSE N'Unknown' END "Single Parent Home?" FROM Registration.Students WHERE LastName LIKE '%an%'; GO This would produce:
Like the other SQL statements, you can also negate this one using the NOT operator.
The % wildcard is used to precede or succeed a specific character or a sub-string. If you want to consider only a range of characters from the alphabet, you can include the range in square brackets. To do this, type [, followed by the lowest character of the range, followed by -, followed by the highest character of the range, followed by ]. For example, to consider the range of letters between p and s, you would use '[p-s]'. Then, either to the left, to the right, or to both sides of this expression, type % to specify whether to include any character or combination of characters before or after the expression. Here is an example: SELECT FirstName [First Name], LastName "Last Name", Gender, [State], CASE SingleParentHome WHEN 1 THEN N'Yes' WHEN 0 THEN N'No' ELSE N'Unknown' END "Single Parent Home?" FROM Registration.Students WHERE LastName LIKE N'%[p-s]' In this case, the result would be a list of students whose last names end with p, q, r, or s. This would produce:
Notice that the list includes only the students whose last names end with a letter between p and s.
As opposed to considering the characters that are in a specific range, to specify a character or a range of characters that must NOT be considered, use the ^ character inside the square brackets but before the desired range. Here is an example: SELECT FirstName, LastName, Gender, SingleParentHome FROM Registration.Students WHERE (LastName LIKE N'%[^p-r]') The result would be a list of students whose last name end with a letter other than p, q, r, or s. Once again, remember that you can negate an expression by preceding it with NOT. Note that if you negate an expression that include ^, you would get the same result as not using ^.
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