SQL: Expert Guides and Resources

SQL is a popular and useful programming language. You can make SQL even more useful if you know the phases of SQL development, the criteria for normal forms, the data types used by SQL, a little bit about set and value functions, as well as some tips on how to filter tables with WHERE clauses.Phases of SQL system developmentIn developing any system, you start at the beginning and go through to the end, and it’s no different with SQL.

To ensure that database tables are designed in such a way that they will hold your data reliably, you need to be sure that they are not subject to modification anomalies. Normalizing your databases will give you that assurance. Compare the SQL criteria in the following list to the tables in your database. Doing so will alert you to the possibility of anomalies, when you find that your database is not sufficiently normalized.

Depending on their histories, different SQL implementations support a variety of data types. The SQL specification recognizes nine predefined general types, shown in the lists below.Exact Numerics: INTEGER SMALLINT BIGINT NUMERIC DECIMAL DECFLOAT Approximate Numerics: REAL DOUB

This Cheat Sheet consists of several helpful tables and lists, containing information that comes up repeatedly when working with structured query language (SQL). In one place, you can get a quick answer to a number of different questions that frequently arise during an SQL development effort.SQL criteria for normal formsTo ensure that database tables are designed in such a way that they will hold your data reliably, you need to be sure that they are not subject to modification anomalies.

SQL gives you options for retrieving, analyzing, and displaying the information you need with the GROUP BY, HAVING, and ORDER BY clauses. Here are some examples of how you can use them. GROUP BY clauses Sometimes, rather than retrieving individual records, you want to know something about a group of records. The GROUP BY clause is the tool you need.

Whether you’re working with Access or a full-featured enterprise-level DBMS — like Microsoft SQL Server, Oracle, or IBM DB2 — to create a table with SQL, you must enter the same information that you’d enter if you created the table with a RAD tool.The difference is that the RAD tool helps you by providing a visual interface — in the form of a table-creation dialog box (or some similar data-entry skeleton) — and by preventing you from entering invalid field names, types, or sizes.

After you create a database in SQL, the next step is to fill it with data. The next step after that is to wait around until there's a need for some particular bit of information contained somewhere in that data, like a needle in a haystack. When the time comes and you want to find that needle, you can use SQL's Data Manipulation Language (DML) to perform a virtual needle extraction.

There are three sources of modification anomalies in SQL These are defined as first, second, and third normal forms (1NF, 2NF, 3NF). These normal forms act as remedies to modification anomalies. First normal form To be in first normal form (1NF), a table must have the following qualities: The table is two-dimensional with rows and columns.