The itemNumber column provides a unique identity for each item (or row) and has an attached column-level constraint that enforces a valid value to always be supplied (NOT NULL).

itemNumber 列提供了每个商品（或列）的惟一标识，它上面还有列级约束，强制要求提供正确的值（NOT NULL）。

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Syscat.references Contains a row for each referential constraint db2 select constname, tabname, refkeyname, reftabname, colcount, deleterule, updaterule from syscat.references.

references为每个参照约束保持一个行db2 select constname, tabname, refkeyname, reftabname, colcount, deleterule, updaterule from syscat . references。

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Syscat.tabconst Contains a row for each unique (u), primary key (p), foreign key (f), or table check (k) constraint db2 select constname, tabname, type from syscat.tabconst.

tabconst为每个唯一性(U)、主键(p)、外键(f)或者表检查(K)约束保持一个行db2 select constname, tabname, type from syscat . tabconst。

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