理解数据库索引的领头部分
本文深入探讨了数据库索引中领头部分的概念，包括如何创建索引及其组成部分，详细解释了不同组合列在索引中的角色。
A leading portion of an index is a set of one or more columns that were specified first and consecutively in the list of columns in the CREATE INDEX statement that created the index. Consider this CREATE INDEX statement:
CREATE INDEX comp_ind ON table1(x, y, z);
x, xy, and xyz combinations of columns are leading portions of the index
yz, y, and z combinations of columns are not leading portions of the index
CREATE INDEX comp_ind ON table1(x, y, z);
x, xy, and xyz combinations of columns are leading portions of the index
yz, y, and z combinations of columns are not leading portions of the index
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