Shulou(Shulou.com)06/01 Report--

Preface

I happened to encounter this knowledge point when I was preparing for the exam recently. I think the difference between char and varchar2 can be distinguished from the three criteria (space complexity, time complexity, stability) of the evaluation algorithm, just mark.

Identical point

Both char and varchar2 are used to store characters.

Differences

Memory consumption

Char is fixed-length character data, the length is in bytes, the minimum and default length is 1, and the maximum length is 2000. Varchar2 is character data with varying length, with a minimum length of 1 and a maximum length of 4000. The length of the varchar2 depends on the length of the stored string, the char is a fixed length, and the excess is filled with spaces. Varchar2 saves more space than char.

Efficiency

When using varchar2, Oracle needs parsing to analyze how many characters there are in this field, so a little slower char is a little more efficient than varchar2 (space for time)

Stability.

If a varchar2 column is often modified, and the length of the data to be modified each time is different, it will cause "row migration" phenomenon, resulting in redundant IUnio, which should be avoided when designing the database. In this case, it would be better to use char instead of varchar2. Hit the point.

When the field we query uses fixed-length character data, we need to pay attention to the format. The string length of the query needs to be equal to the length of the data type, otherwise the data cannot be found.

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