Mysql should i use text or varchar

Using a separate table can help you avoid query cache invalidations and lets you use some of the more advanced techniques we show in this section. To keep things as simple as possible, suppose you have a counter table with a single row that just counts hits on your website:. It will serialize those transactions. You can get higher concurrency by keeping more than one row and updating a random row. This requires the following change to the table:. Prepopulate the table by adding rows to it. Now the query can just choose a random slot and update it:.

A common requirement is to start new counters every so often for example, once a day. If you need to do this, you can change the schema slightly:. If you want to reduce the number of rows to keep the table smaller, you can write a periodic job that merges all the results into slot 0 and deletes every other slot:. You also increase development complexity for both read and write operations.

MySQL performs most alterations by making an empty table with the desired new structure, inserting all the data from the old table into the new one, and deleting the old table. Recent versions of InnoDB [ 48 ] also support building indexes by sorting, which makes building indexes much faster and results in a compact index layout.

The technique for a shadow copy is to build a new table with the desired structure beside the existing one, and then perform a rename and drop to swap the two. If you are using Flexviews discussed in Materialized Views , you can perform nonblocking schema changes with its CDC utility too. In theory, MySQL could have skipped building a new table. This statement modifies the. As a result, it is very fast.

Use it at your own risk. We advise you to back up your data first! If you remove a constant and some rows contain that value, queries will return the value as the empty string. The basic technique is to create a. Create an empty table with exactly the same layout , except for the desired modification such as added ENUM constants. This will close all tables in use and prevent any tables from being opened.

The current column looks like this:. Now we swap the. Back in the MySQL prompt, we can now unlock the table and see that the changes took effect:. The usual trick for loading MyISAM tables efficiently is to disable keys, load the data, and reenable the keys:.

This works because it lets MyISAM delay building the keys until all the data is loaded, at which point it can build the indexes by sorting. This is much faster and results in a defragmented, compact index tree. MyISAM builds unique indexes in memory and checks the uniqueness as it loads each row. This calls for dropping all of the nonunique indexes, adding the new column, and then adding back the indexes you dropped.

Percona Server supports doing this automatically. Again, this is an undocumented, unsupported technique. Use it at your own risk, and back up your data first. Load the data into the table to build the. MYD file. Create another empty table with the desired structure, this time including the indexes. This will create the. MYI files you need. This will build all indexes by sorting, including the unique indexes.

This procedure can be much faster for very large tables. Good schema design is pretty universal, but of course MySQL has special implementation details to consider. MySQL likes simplicity, and so will the people who have to work with your database:. Try to avoid extremes in your design, such as a schema that will force enormously complex queries, or tables with oodles and oodles of columns.

An oodle is somewhere between a scad and a gazillion. Watch out for variable-length strings, which might cause pessimistic full-length memory allocation for temporary tables and sorting. Avoid the legacy MySQL-isms such as specifying precisions for floating-point numbers or display widths for integers.

BIT is best avoided. Normalization is good, but denormalization duplication of data, in most cases is sometimes actually necessary and beneficial. And precomputing, caching, or generating summary tables can also be a big win. A multibyte character set can require more than one byte to store each character. All three do different things. Skip to main content. Start your free trial. Chapter 4. Optimizing Schema and Data Types.

Choosing Optimal Data Types. Smaller is usually better. Simple is good. Avoid NULL if possible. Whole Numbers. Real Numbers. String Types. Generosity Can Be Unwise. Using ENUM instead of a string type. Table Date and Time Types. Bit-Packed Data Types. Bitwise operations on integer columns An alternative to SET is to use an integer as a packed set of bits. Choosing Identifiers. String types Avoid string types for identifiers if possible, because they take up a lot of space and are generally slower than integer types.

Beware of Autogenerated Schemas. Special Types of Data. Normalization and Denormalization. Pros and Cons of a Normalized Schema. Normalized updates are usually faster than denormalized updates. Pros and Cons of a Denormalized Schema. A Mixture of Normalized and Denormalized. Cache and Summary Tables. You can read more about managing database with cPanel in:. As always, if you have any feedback or comments, please let us know.

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Toggle navigation All Blog. Of course, that's only if performance matters to you. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Is there any reason to use varchar over text columns in a database? Ask Question. Asked 9 years, 4 months ago. Active 2 years, 5 months ago. Viewed 44k times. Improve this question.

Oded Izkata Izkata 5, 5 5 gold badges 23 23 silver badges 43 43 bronze badges. At least for SQL Server , text is deprecated. There are also considerations of usage that are related to where the data is stored and how it therefore gets accessed. On some DBMSs you may not be able to use a text column in a sort or where clause. I'm not familiar with Postgres but check your documentation.

This StackOverflow question might provide some more info. Add a comment. BLOB s are used to store data files like images, videos, and executables. There are many database diagramming tools that are not only incredibly useful but also free.

After launching and connecting to SQL Server Management Studio, create a new login and select the database that is connected to Chartio. Download our free cloud data management ebook and learn how to manage your data stack and set up processes to get the most our of your data in your organization. Data Tutorials.