Select command is used to collect date from the table. We will discuss more on this by adding more commands to this select command. Understand Structured Query Language ( SQL ) and read the basics of database table here.
SELECT query with LIMIT and order by with WHERE condition checking using BETWEEN range
20 SELECT queries with WHERE BETWEEN AND OR IN LIKE commands to get data from SQLite database Full student table with SQL Dump Now your table with some data is ready. We will apply select command to our table ( name student ) and fetch all the records SELECT * FROM `student`
SELECT * FROM `student` LIMIT 0,3
Related Tutorial Copy data to new table SQL Left Join SQL UNION This command with LIMIT command will return us 3 records starting from 0 ( or first ) record. This is very important when we use this command with ORDER BY command. Now let us try to list all the students who have come in first 3 ranks. We are required to list here 3 records who have mark more than the others. The top 3 students we want to display in order of first, second and third. The order we can display are in by default in ascending order but we require the listing should return in descending order so we will get the highest ranked student at the top. Before that let us start with a simple example of ORDER BY command.SELECT * FROM `student` ORDER BY mark This will display the records of students in the order of lowest mark to highest mark.
SELECT * FROM `student` ORDER BY `mark` DESC With the addition of command DESC we can change the order of display to keep the highest mark at the top of the list and lowest mark at the bottom of the list. Now let us add the LIMIT command to display only the top 3 records. We already have the list in the order of highest mark to lowest mark so by just limiting the number of records to 3 will give our required top three student records. SELECT * FROM `student` ORDER BY `mark` DESC LIMIT 0,3
Combining two columns and displaying them as oneWe can use CONCAT function to combine two columns and displaying them as one column. For example we can combine first name and last name and display them as Name.Sample code in PHPWe have to first connect to database using PHP PDO. Then we can display the records by looping. Here is the sample code to display 4 records. However any other query can be used and matching records can be displayed. <?Php require "config.php";// Database connection $count="SELECT * FROM student LIMIT 0,4"; echo "<table>"; echo "<tr><th>id</th><th>name</th><th>class</th> <th>mark</th></tr>"; foreach ($dbo->query($count) as $row) { echo "<tr ><td>$row[id]</td><td>$row[name]</td> <td>$row[class]</td><td>$row[mark]</td></tr>"; } echo "</table>"; ?> Full student table with SQL Dump←What is SQL Query with WHERE Condition→ Collecting data by linking more than one table → This article is written by plus2net.com team. https://www.plus2net.com plus2net.com ▼ More on getting records from table with different combinations of commands
When you want to select specific data from one or more sources, you can use a select query. A select query helps you retrieve only the data that you want, and also helps you combine data from several data sources. You can use tables and other select queries as data sources for a select query. This topic provides an overview of select queries, and gives steps for creating a select query, by using the Query Wizard or in Design view. If you want to use the Northwind sample database to learn more about how queries work, see the article Introduction to queries. When you want to use data, you rarely want to use all of the data from one table. For example, when you want to use data from a Contacts table, you usually want to look at one specific record, or maybe just the telephone number. Sometimes you want to combine data from more than one table, such as combining Customer information with Order information. To select the data that you want to use, you use a select query. A select query is a database object that shows information in Datasheet view. A query does not store data, it displays data that is stored in tables. A query can show data from one or more tables, from other queries, or from a combination of the two. A query lets you:
You can create a select query by using the Query Wizard or by working in Design view. Some design elements are not available when you use the wizard, but you can add these elements later by using Design view. Although the two methods are somewhat different from each other, the basic steps are essentially the same:
After you have created a select query, you run it to see the results. To run a select query, you open it in Datasheet view. If you save the query, you can reuse it whenever you need, for example, as a data source for a form, report, or another query. You can use the Query Wizard to automatically create a select query. When you use the wizard, you have less control over the details of the query design, but the query is usually created faster than if you did not use the wizard. Moreover, the wizard can catch some simple design mistakes and prompt you to perform a different action. If you use fields from data sources that are not related to each other, the Query Wizard asks you if you want to create relationships. The wizard opens the Relationships window for you, but you must restart the wizard if you edit any relationships. Therefore, before you run the wizard, consider creating any relationships that your query needs. For more information about creating table relationships, see the article Guide to table relationships.
Top of Page You can use Design view to manually create a select query. When you use Design view, you have more control over the details of the query design, but it is easier to make design mistakes, and it can take longer than using the wizard. When you use Design view, to add data sources, you add the data sources and fields in separate steps. However, you can always add more data sources later if you want.
When you add the data sources, if the sources already have relationships defined between them, those relationships are automatically added to the query as joins. Joins specify how data from related sources should be combined. Access also automatically creates a join between two tables if they have fields have compatible data types and one field is a primary key. You might want to adjust the joins that Access creates. Access determines what type of join to create based on the relationship the join represents. If Access creates a join but there is no defined relationship, Access creates an inner join. If Access automatically creates the correct joins when you add the data sources, you can skip ahead to Step 3: Add output fields. In some cases, you want to join two copies of the same table or query, called a self-join, that combines records from the same table when there are matching values in the joined fields. For example, say you have an Employees table in which the ReportsTo field for each employee's record displays his or her manager's ID instead of name. You could use a self-join to display the manager's name in each employee's record instead. When you add a data source a second time, Access appends _1 to the name of the second instance. For example, if you added the Employees table twice, the second instance would be named Employees_1. If the data sources that you add to a query already have relationships, Access automatically creates an inner join for each relationship. If referential integrity is enforced, Access also displays a "1" above the join line to show which table is on the "one" side of a one-to-many relationship and an infinity symbol (∞) to show which table is on the "many" side. If you add queries to your query, and have not created relationships between those queries, Access does not automatically create joins between those queries, or between queries and tables that are not related. If Access does not create joins when you add data sources, you should usually add them yourself. Data sources that are not joined to any other data source can cause problems with the query results. You might also want to change the type of a join from an inner join to an outer join, so that your query includes more records.
After the joins are ready, you add output fields — fields that have data that you want in the query results. You can easily add a field from any of the data sources that you added in step 1.
If you want to perform calculations or use a function to produce query output, you can use an expression as an output field. An expression can use data from any of the query data sources, as well as functions, such as Format or InStr, and can also contains constants and arithmetic operators.
This step is optional. You use criteria to limit the records that your query returns, on the basis of whether field values meet the criteria that you specify.
You can use criteria with multiple fields. When you do, all the criteria in a given Criteria or Or row must be true for the record to be included. You can add a field to your query design and not include the field's data in the query output. You do this if you want to use the field's values to limit the query results, but don't want to see the field values.
This step is optional. You might want to summarize data, especially if your data is numeric. For example, you might want to see the average price, or total sales. To summarize data in a query, you use the Total row. By default, the Total row is not displayed in Design view.
To see the query results, on the Design tab, click Run. Access displays the results of your query in Datasheet view. To make further changes to the query, click Home > View > Design View to switch back to Design view. Change your fields, expressions, or criteria and rerun the query until it returns the data that you want. Top of Page |