Add example for multi argument CHAR() (#16957)

[ti-chi-bot]

This is an automated cherry-pick of #16957

What is changed, added or deleted? (Required)

ref #15417

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[qiancai]

/approve

[hfxsd]

/approve

[hfxsd]

/approve

[hfxsd]

/approve

[ti-chi-bot]

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