How to query a table in oracle

<p>Oracle Query a certain table</p> <p>Oracle is a widely used relational database management system that can help users store, manage and retrieve data in other database processes. When working with Oracle, one of the most basic operations is querying a table. Next, this article will introduce how to query a table. </p> <p>Querying a single table</p> <p>Oracle can query a table through SQL statements, among which the most basic query statement is the SELECT statement. This statement helps you select data from one or more tables and return it to the user. Here is an example of querying a single table: </p> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">SELECT * FROM table_name;</pre><div class="contentsignin">Copy after login</div></div> <p>With the above statement, we can select all data from a table called <code>table_name</code>. If you need to return a specific column in the list, you can replace <code>*</code> with the column name. For example: </p> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">SELECT column1, column2, column3 FROM table_name;</pre><div class="contentsignin">Copy after login</div></div> <p>Query multiple tables</p> <p>In addition to querying a single table, Oracle can also query multiple tables. In this case, a join statement is required. A join statement joins data from two or more tables and returns data based on a specified relationship. The following is an example of a join statement: </p> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">SELECT * FROM table1 INNER JOIN table2 ON table1.column_name = table2.column_name;</pre><div class="contentsignin">Copy after login</div></div> <p>With the above statement, we establish a join between two tables named <code>table1</code> and <code>table2</code> and pass the column name<code>column_name</code> Compare them. INNER JOIN is the default join type for returning matching rows from two tables. If you need to return all rows, including unmatched rows, you can use OUTER JOIN. </p> <p>Sort results</p> <p>When the query results contain multiple rows, the results can be sorted in a specific order. To sort the results with an ORDER BY statement, you need to specify one or more column names and a sort order. For example, the following statement can be used to sort the results in ascending order: </p> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">SELECT * FROM table_name ORDER BY column_name ASC;</pre><div class="contentsignin">Copy after login</div></div> <p>In the above statement, we have used the <code>ORDER BY</code> clause to sort the results in ascending order. If you need to sort in descending order, you can use the <code>DESC</code> keyword. </p> <p>Filter results</p> <p>During the query process, you can filter the returned results through the WHERE clause. This clause helps you filter query results based on specific criteria. For example: </p> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">SELECT * FROM table_name WHERE column_name = 'value';</pre><div class="contentsignin">Copy after login</div></div> <p>In the above statement, we use the WHERE clause to filter the <code>column_name</code> with the value <code>'value'</code> in the <code>table_name</code> table. In addition to the <code>=</code> operator, you can also use other operators to filter, such as <code>></code>, <code><</code>, <code>>=</code>, <code><=</code> and <code><></code>. </p> <p>Conclusion</p> <p>In Oracle, you can easily query data in one or more tables using the SELECT statement. When making queries, you can use statements such as joins, sorting, and filtering to obtain more precise and meaningful results. Mastering the relevant SQL statements can help you query the data in the table more efficiently. </p>

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