By Clare Churcher
Clare Churcher's Beginning SQL Queries is your advisor to studying the lingua franca of the database undefined: the SQL language. sturdy wisdom of SQL is important to someone operating with databases, since it is with SQL that you simply retrieve info, manage info, and generate company effects. realizing find out how to write stable queries is the basis for all paintings performed in SQL, and it's a starting place that Clare lays good in her publication.
- Does no longer bore with syntax!
- Helps you examine the underlying suggestions considering querying a database, and from there the syntax is simple
- Provides particularly transparent examples and motives
- Is academically sound whereas being functional and approachable
Read Online or Download Beginning SQL Queries: From Novice to Professional PDF
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Additional resources for Beginning SQL Queries: From Novice to Professional
Performing Simple Counts As well as retrieving a subset of rows and columns from a table, we can also use SQL queries to retrieve some statistics. There are SQL functions that allow us to count records, total or average values, find maximum and minimum values, and so on. In this section, we will look at some simple queries for counting records. ) 3. ” 35 36 CHAPTER 2 ■ SIMPLE QUERIES ON ONE TABLE Listing 2-24 shows a simple query to return the number of records in the Member table. COUNT is a function in SQL, and * means count each record.
To answer the question about who has entered both competitions, we need to look at more than one row of the Entry table at the same time (that is, two fingers). If we have two fingers, one pointing at the row shown in Figure 2-10 and another pointing at the previous row, then we can deduce that 415 has been in both tournaments. We’ll look at how to do this in Chapter 5. CH A PT ER 2 ■ S IMP L E QUER IES O N O NE T AB LE Misusing Select Operations to Answer Questions with the Word “not” Now let’s consider another common error.
For example, they are both integers or both dates. Different database products may interpret join compatibility differently. Some might let you join on a float (number with a decimal point) in one table and an integer in another. Some may be fussy about whether text fields are the same length (such as CHAR(10) or CHAR(15)), and others may not. I recommend you don’t try to join on fields with different types unless you are very clear what your particular product does. As always, the best thing is to make sure that when you design your tables, those fields that are likely to be joined have the same types.
Beginning SQL Queries: From Novice to Professional by Clare Churcher