SQL constraints the data that can be in a table. A violation of a constraint causes an action to be aborted. Constraints can be defined upon creation or using the ALTER TABLE statement once created. The general syntax of a CREATE (or use ALTER instead of CREATE) when defining constraints is as follows: CREATE TABLE tablename ( columnname datatype(size) constraintname, columnname datatype(size) constraintname, columnname datatype(size) constraintname, columnname datatype(size) constraint name, columnname datatype(size) constraint name, ); Obviously, replace columnname with the name of each of your column, datatype with the types of data your column contains and constraint name with the constraint you wish to use. You have the following constraints…
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User And Permissions Management In MySQL
By default, MySQL comes with a root user configured. You can also create additional users, change passwords for users, and assign what databases and tables they have access to. From MySQL, you can can create a basic user using the CREATE USER statement, providing a user, a location, and then using IDENTIFIED BY followed by a password. In production, this would look similar to the following, using krypted as the user and mysecretpassword as the password: CREATE USER 'krypted'@'localhost' IDENTIFIED BY 'mysecretpassword'; Once you’ve created a user, you’ll want to assign what the user can access. Here, the * wildcard is pretty handy. In the following command, we’ll use the…
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Install MySQL On OS X
OS X might be the easiest platform to install MySQL on. To do so, simply download the MySQL installation package from the MySQL Download site. I like to use the third link (the DMG). Once downloaded, run the package. The package will ask you a few questions and you can easily just select the default choice during the installation process. Once installed, you’ll be prompted that a temporary password has been used for your MySQL instance. The password will get you in the first time, so you can change it. Once you have documented the password, open System Preferences and click on MySQL in the bottom row of System Preference Panes. Click Start…
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Use SELECT INTO To Copy Data Between Tables
You can use the SELECT INTO statement finds data and then copies that data between tables or databases. To do so, use the following syntax: SELECT * INTO newtablename FROM tablename; So to copy that Customers table to a new table called Customers2: SELECT * INTO Customers2 FROM Customers; Or to copy only certain columns into Customers2, we’d use the following: SELECT ID,Site INTO Customers2 FROM Customers;
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Create A SQL Database
So you’re ready to write some software? Or test some cool stuff. Or build something awesome. You can use the CREATE DATABASE statement to get started, by creating a database. To do so is pretty easy, simply run that statement followed by a name for the database (called Customers): CREATE DATABASE Customers; Once you’ve created a database, it’s time to create tables, which can be done using the CREATE TABLE statement. The Syntax of that statement looks something like this, defining a set of columns, their data type and the size of the column (in the form of a maximum length), all wrapped in parenthesis with each column separated by…
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Remove Records From A MySQL Database
Sometimes you have data in a MySQL database that you just don’t need. You can delete tables and records pretty easily. In fact, it’s almost too easy. And there’s no undo. So be careful. And backup. And then backup again. And then snapshot again, before tinkerating with anything in this article. In this article we’ll look at using the SQL DELETE statement to delete rows in a table. To do so, we’ll follow this basic syntax, which includes a WHERE clause to narrow the scope of the DELETE by specifying which records will be removed: DELETE FROM table WHERE column=value; In this article, we’ll use the same “Customers” table from…
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Update Existing SQL Records Using the UPDATE Statement
Previously we looked at finding data in a SQL database and The UPDATE statement is used to update records in a table. You can also use the UPDATE statement to update existing records in a table. When using the SQL UPDATE statement, we’ll also use the WHERE clause, as we used previously to constrain output of a SELECT statement. The WHERE locates the record(s) to be updated with syntax as follows: UPDATE table SET column=value,column=value,... WHERE column=value; The WHERE clause indicates the record(s) to update. I’ve forgotten to put it in in the past and updated every record of a database. That’s bad (unless you mean to do it). So…
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Add New Records To MySQL Databases With The INSERT Statement
Sometimes you need to write a record into a table in a SQL database. The INSERT INTO statement creates new records in a table and can work in one of two ways. The first form does not specify the column names where the data will be inserted, only their values. When doing so, each value needs to be inserted in the columned order they appear, here the table being the name of the table you’re adding a record into and each value would be replaced with the contents of your value (don’t insert the string ‘value’ into each!): INSERT INTO table VALUES (value,value,value,...); If you don’t have every value to…
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Compound Searches With SQL Using AND && OR
Previously, we looked at the SQL SELECT and WHERE options to obtain output and then constrain what would be displayed in a query. The AND & OR operators are used to add additional logic so you can filter records based on more than one condition. Which is to say to search based on the contents of multiple columns within a single table. AND is used to show information if two different conditions are true and OR is used to show information if either condition is true. Below is a selection from the “Customers” table that showed in our first article an we will use it to run some SQL sorting…
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Constrain SQL Queries Using WHERE and LIKE
Previously, we covered the SQL SELECT Statement, to pull data from a SQL database. Here, we’ll constrain our search for items that match a given string, or pattern using the WHERE clause to filter search results, rather than getting all of the records and parsing the output. The WHERE clause extracts records that fulfill a specified string and follows the general syntax as follows, replacing the word column with the name of the column in one of your tables and the word table with the name of a table that you’d like to search within: SQL WHERE Syntax SELECT column,column FROM table WHERE column operator value; Below is a selection…