What is histogram?

A two-dimensional graph where the x-axis represents column ranges and the y-axis represents the number of rows containing the range of values. Histograms support more detailed distribution data than the uniform value assumption. Histograms are part of a table profile. A traditional or equal-width histogram has equal column value widths but a varying number of rows in each bar. An equal-height histogram has variable-size column ranges but approximately equal number of rows in each bar. Most dbmss use equal-height histograms because the maximum and expected estimation error can be easily controlled by increasing the number of ranges.

Tags: Database, Education, Software

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