<html><head><title>PgAccess Tutorial</title></head> <body bgcolor="#C0C0C0"> <h1>PgAccess Tutorial - SELECT</h1> <img src="altern_q.jpg" border=1 align=right> <h2>What is a query?</h2> <em>Query</em> is the term for an SQL command which will perform an operation on a table. It is sometimes confusing to newcomers, as some of the operations seem to have nothing to do with querying in the common sense of <em>asking</em>. As we saw in the previous section, a <em>query</em> can simply copy records from an ASCII file to a table.<p> The PostgreSQL documentation has a complete list of <em>queries</em> that can be used. We'll start with the common task of selecting records with certain characteristics.<p> <h2>Selecting records</h2> <img src="altern_v.jpg" border=1 align=right> Suppose that I want to know all of the references in the sample table <em>psyref</em> for which the word "alternative" appeared in the title.<p> By clicking <em>Query</em>, then <em>New</em>, a <b>Query builder</b> window will appear. Clicking in the area below the buttons will allow the user to enter an SQL <em>query</em>. The specification of the <em>query</em> must be exact or PostgreSQL will return an error message.<p> The <em>query</em> shown will <b>SELECT</b> those records from <em>psyref</em> that contain the word "alternative" anywhere in the <em>title</em> field. The '*' indicates that all of the fields are to be returned. You might only want to return, for instance, the <em>author</em> field if you were only interested in which authors had used that word in the title of their work.<p> At the right is the record that fulfils these conditions, displayed in the <b>Table viewer</b>. If you wanted to save this query for use again, clicking the <em>Save query definition</em> button will do so. You will then see <em>altern</em> listed under <em>Queries</em> when you return to the main window. By clicking the <em>Save this query as a view</em> tickbox in the <b>Query builder</b>, the result of your query will be saved as a <em>View</em> which you can access from <em>Views</em> in the main window. Click the <em>Close</em> button to leave the <b>Query builder</b>.<p> <a href="index.html#tut">Back to index</a> </body></html>
