Type each column once, as early as you dare
· 6 min read
Re-CASTing the same physical column in every medallion layer feels careful. It is usually how drift multiplies. Bronze casts to decimal. Silver casts again "to be safe." Gold casts a third time and invents an unknown literal with yet another type. Consumers inherit a guessing game.
Type each published column once, as early as you dare (usually bronze, sometimes the first stable clean view). Silver and gold keep aliases, business calculations, and typed unknown-row literals only. UNION alignment casts are the exception, not the lifestyle. Lint the rest.
Figure 1. Type each column once, as early as you dare. Downstream layers should inherit the contract, not reinvent CASTs. Source: Microsoft Learn: copy data activity.