Creating a New Schema
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When you open the newly created database object, you see that it contains the public schema by default While it is perfectly acceptable to create data tables and other objects
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Figure 4-4 The CREATE DATABASE SQL statement
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within the public schema, we will create a new schema to hold our application data objects Unlike the public schema, the newly created schema will be protected by default No users will have access to the schema until we specifically grant them access This helps provide better security for the application by default There are a couple of ways to create a new schema in the database The first method is to right-click the newly created database object that will contain the new schema and select New Object | New Schema The second method is to expand the newly created database object, right-click the Schemas object contained within the database object, and select New Schema from the menu Either method opens the New Schema window, shown in Figure 4-5 Just like the New Database window, the New Schema window provides an easy form (Properties tab) for you to fill out to define the new schema You must provide a unique name for the schema within the database in which it is created For this example, use the schema name store Just as with the new database, you must also provide the owner
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Figure 4-5 The New Schema window
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of the schema, which should be set to the postgres user account Unlike the new database, you do not specify the tablespace for the schema PostgreSQL creates the schema object in the same tablespace where the parent database object resides Also unlike the new database, you can supply a comment in the Comment field of the Properties tab Note that the OID field is grayed out PostgreSQL automatically assigns a unique OID to the database once it is created The New Schema window also allows you to assign permissions to the newly created schema By default, only the superuser account has permissions to create and modify data in the schema We will change that later after we create some user accounts After entering the information, click OK to create the new schema The new schema automatically appears within the database object in pgAdmin III You can expand the new schema object to see the listing of objects contained within the schema At this point there should not be any new objects within the schema Now it is time to create some tables
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Creating the Tables
Tables are the meat and potatoes of our database They hold all of the data used in the application As mentioned in 1, in a relational database model, data is divided into tables that contain related information As specified for the example application, we will create three separate tables to hold the data required for this application To create a new table, expand the newly created database object and then the newly created schema object In this listing, right-click the Tables object and select New Table from the menu The New Table window appears, shown in Figure 4-6 There are several steps involved in creating a new table, and you do not necessarily have to perform them all at the same time The first tab is the Properties tab Just as with the New Database and New Schema windows, this tab is where you define the basic properties for the new table There are a few rules for defining table names in PostgreSQL: Must be unique within a schema Must start with a letter or an underscore (_)
Figure 4-6 The New Table window
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Subsequent characters can be letters, numbers, underscore, or a dollar sign ($) Must be 63 or fewer characters long Case sensitive The last rule is often what gets novice database administrators in trouble This means that you can have a table named Customer as well as another table named customer in the same schema This is almost always a recipe for disaster when running SQL statements, and should be avoided if at all possible For this exercise, we will capitalize the first character in the table names and make the rest lowercase When creating this new table, use the name Customer As with the other database objects, you must define the owner of the table Again, we will use the postgres user for this exercise When creating a new table, you must specify the tablespace where the table will be stored You may store tables in different tablespaces within the same database if you desire For this exercise, you should just use the pg_default tablespace The Has OIDs check box indicates whether PostgreSQL will assign an object ID (OID) to the newly created table By default, PostgreSQL does not assign an OID to user-created tables If you plan on using the PostgreSQL inheritance feature (discussed in 1), you must assign an OID to the table Since our tables will not use this feature, we can leave this check box unchecked The Inherits from Tables section allows you to specify whether the newly created table will inherit any columns (fields) from parent tables The parent table must have an OID assigned to it Again, since none of our tables will do this, we will leave this section blank Finally, the Comment section allows us to place a comment in the table that can be seen from pgAdmin III when we view the properties of the table This is extremely handy when designing a large system with lots of tables After filling in the required information in the Properties tab, click the OK button to create the table The new table appears under the Tables list in the new schema You have created a new table, but there is no data defined within the table We will do that shortly Before entering new data, look at the table objects created with the new table Expand the new Customer table object that was created in the new schema Each table consists of five categories of objects: Columns Hold data elements in the table Constraints Add further restrictions on data in the columns Indexes Speed up data searching in the table Rules Define functions performed on data in other tables based on events Triggers Define functions performed on data in the table based on events The next step to complete your table is to define columns for the data Each column defines a data element that will be stored in the table Each column must be declared as