May 2018
Intermediate to advanced
576 pages
30h 25m
English
Finding a unique key is possible for a program, but in most cases, a human can do this much faster by looking at things such as column names, foreign keys, or business understanding to reduce the number of searches required by the brute-force approach.
The ANALYZE command works by taking a sample of the table data, and then performing a statistical analysis of the results. The n_distinct value has two different meanings, depending on its sign: if positive, it is the estimate of the number of distinct values for the column; if negative, it is the estimate of the density of such distinct values, with the sign changed. For example, n_distinct = -0.2 means that a table of one million rows is expected to have 200,000 distinct values, ...