…ain const nullable column

…ain const nullable column

Fix bug in if function when then clause contain const nullable column

(cherry picked from commit 336430d)

…ain const nullable column

…ain const nullable column

Backport #14646 to 20.9: Fix bug in if function when then clause contain const nullable column

Backport #14646 to 20.8: Fix bug in if function when then clause contain const nullable column

Backport #14646 to 20.6: Fix bug in if function when then clause contain const nullable column

Backport #14646 to 20.7: Fix bug in if function when then clause contain const nullable column

* master: (375 commits)
  Update type-conversion-functions.md
  Update maxmap.md
  Update maxmap.md
  Update maxmap.md
  Update single_fixed_string_groupby.xml
  Alter remove column properties and TTLs (ClickHouse#14742)
  better fixed string group by support
  Fix incorrect key condition of fixed strings.
  constant output order
  more tests for  ClickHouse#14646
  Maybe fix MSan report in base64
  Proper exception message for wrong number of arguments of CAST
  Added a test
  Fix buffer overflow in "bar" function
  Update convertMySQLDataType.cpp
  Fix clang-tidy
  Remove obsolete code from performance test
  Slightly better code
  Even more
  Even more
  ...

# Conflicts:
#	src/Interpreters/Context.cpp

* ldap-any-user-authentication: (781 commits)
  Remove extra declaration
  Synchronize the code with respect to IAccessStorage::login() functionality
  Update type-conversion-functions.md
  Update maxmap.md
  Update maxmap.md
  Update maxmap.md
  Update single_fixed_string_groupby.xml
  Alter remove column properties and TTLs (ClickHouse#14742)
  better fixed string group by support
  Fix incorrect key condition of fixed strings.
  constant output order
  more tests for  ClickHouse#14646
  Maybe fix MSan report in base64
  Proper exception message for wrong number of arguments of CAST
  Added a test
  Fix buffer overflow in "bar" function
  Update convertMySQLDataType.cpp
  Fix clang-tidy
  Remove obsolete code from performance test
  Slightly better code
  ...

# Conflicts:
#	src/Access/ContextAccess.cpp
#	src/Access/ContextAccess.h
#	src/Access/ExternalAuthenticators.h
#	src/Access/LDAPAccessStorage.cpp
#	src/Access/LDAPClient.h
#	src/Access/LDAPParams.h
#	src/Common/ErrorCodes.cpp
#	src/Interpreters/Context.cpp
#	src/Interpreters/Context.h